It might be useful to have more information about a monitor when
configuring its settings in the Options menu. Therefore, this commit
adds support for showing additional information about a monitor
(resolution and platform-specific name).

There are no guarantees from the WM that calling `fullscreen_screens`
with all monitor indices set to `-1` results in the window's current
monitor being used. Because FullScreenMode uses the word "current"
we want to explicitly ask the WM to use that monitor.

The user might not always want to use all monitors when in fullscreen
mode, but instead only a few. This commit adds support for configuring
selected monitors from command line, in the config file and graphically
in the options menu.

Because it might be hard to guarantee the consistency of monitor
identifiers coming from third-parties (for example FLTK), it has been
decided to use our own numerical identifier. This identifier is based on
the monitor's positions. The mapping between this identifier and the
indices used by FLTK is done by MonitorIndicesParameter.

Before this commit, `FullScreen` and `FullScreenAllMonitors` could be
used to configure whether to use the current monitor in fullscreen,
or all monitors in fullscreen.

This commit deprecates `FullScreenAllMonitors` in favour of
`FullScreenMode` (which can either be `current` or `all`). This allows
for additional modes to be added, without the risk of having invalid
states (for example two activate two different fullscreen modes at the
same time).

A new concept has been added; read-only parameters. They are parameters
that will be read, but never written back. This allows for migration
paths to be constructed, where a parameter can be taken to consideration
but then for example be discarded, logged or changed into something else.

This has been used for `FullScreenAllMonitors` to provide a migration
path. On startup of vncviewer, if `FullScreenAllMonitors` is enabled,
`FullScreenMode=all` will be automatically enabled instead. The next
time the configuration file is written to disk, `FullScreenAllMonitors`
will then be removed.

Previously, it was assumed that all monitors (and especially the primary
monitor, index 0) was inside the window when we calculate the position
of the overlay.

That might not always be the case, for example when using fullscreen
mode over a narrower set of monitors. This commit does so the overlay is
positioned correctly based on the actual window size, instead of what we
expect it to be.

cocoa_capture_displays it captures all displays enclosed by the
window_rect. If a set of displays were captured, but the configuration of
what monitors to use changed, a second call would only add to the set
of captured displays. Therefore, if the user enabled
FullScreenAllMonitors (all displays captured) and then disabled it (only
one display captured) they would get into a state were monitors not used
for the VNC session still were captured (which on macOS for example,
results in displays being unusable for other things).

This has now been fixed, resulting in monitors outside the window_rect
not being unnecessarily captured.

The call of gnutls_set_default_priority_append() expects a normal priority
string, which means it must not start with ':'.

It was only possible to capture either the current, or all displays
previously. This could become an issue if you want to show a vnc session
over only a selected set of displays, because then we only want to
capture those displays.

The solution in the commit was chosen because it handles all cases - by
looking at what monitors are enclosed by the viewport the implementation
is independent on any configuration, but instead captures the monitors
actually being used.

Without this change I get CMake errors due to use of ${FLTK_INCLUDE_DIR}
and references to the non-existent vncviewer target.

I am cross-compiling from macOS for a FreeBSD-derived system so my host
file system is case insensitive but the target isn't. Without this change
I get the following warnings which show that the vnc "Input.h" is being
included from mi/mi.h instead of the xserver "input.h":
```
In file included from /Users/alex/cheri/xvnc-server/hw/vnc/Input.c:33:
/Users/alex/cheri/xvnc-server/mi/mi.h:55:10: warning: non-portable path to file '"Input.h"'; specified path differs in case from file name on disk [-Wnonportable-include-path]
#include "input.h"
         ^~~~~~~~~
         "Input.h"
```

Some operating systems such as FreeBSD don't define a HOST_NAME_MAX
macro. The portable approach to determine the real host name limit is
calling sysconf(_SC_HOST_NAME_MAX) so do that instead.

Xvnc was originally based on Xvfb, but it's just confusing to keep the
names. So change all prefix to "vnc" instead to clearly mark things as
part of TigerVNC.

It isn't really useful as it behaves just like starting multiple
servers, so remove it in favour of keeping things simple.

This is a development flag with no real use, so remove it to clean up
the code.

Remove stuff we don't use, and get it more in sync with Xvfb for easier
comparison.

This was removed years ago.

The memory leak this worked around was fixed in X.org 1.16.

Keep everything in one place to make it easier to read.

This also removes the call to RRInit() as that is done implicitly
anyway.

There's been a common one since X.org 1.11, so use that instead of our
own copy.

We don't build for that platform anyway, so this is just a remnant from
Xvfb.

With the 1.20.x releases there has been features and API changes even on
patch level versions, so we need to update our macros to handle these as
well.

This is a pointless remnant of Xvfb. We never print the id of the shared
memory, so no other application can access this memory anyway.

This hasn't been supported or used in many years, so clean out the final
remnants.

This hasn't been used since xorg-server 1.1 so get rid of it.

This is consistent with other ddx behaviour.

This is what all the other ddx variants use, so do the same in Xvnc to
be consistent.

Makes it easier to compare with upstream files as the formatting will be
the same.

RENDER has been mandatory since xorg-server 1.9, so remove these
checks.

This should only be in the ddx parts of an X server, and Input.c is used
by libvnc.so as well and can cause conflicts there.

This was removed from Ubunut's X.org packages years ago, so drop it from
our packing as well.

We miscalculated the screen layout if the geometry had an offset as we
adjusted the real screen layout to account for the offset, but compared
it to the unadjusted geometry.

Is a lot more useful default than the previous "x11", or "x0vncserver".
At the same time give x0vncserver a parameter to change the name.

Let's avoid making this too complex and force every user to know about
magical functions.

Allows the default value to be dynamically generated in a buffer that is
reused.

Better to just hide these parameters rather than stating that they are
unused in the man page.

Our current architecture doesn't support waiting for a response here, so
don't even try or we'll just get an error.

The session might have died, or failed to initialise properly, so be
prepared for gnutls_bye() to be unable to do its job.

We would leak the security module below the top client VeNCrypt module,
meaning that those modules would not get a chance to shut down
gracefully.