Shift key handling was improved in 30b3f92, but the test documentation
wasn't updated.

Improve AltGr detection even further on Windows so we can detect the
case when Ctrl and AltGr are pressed together.

Try to properly detect the fake CtrlL+AltR sequence Windows sends
when pressing AltGr. This allows us to send more accurate key
events over to the server.

Add some more dead keys that we've noticed, and clarify the naming
on some existing ones.

We now treat Meta as an independent key, so make sure our test
routines actually verify that it works.

Since 83e019f599.

This key requires a bit extra care on Windows. We get wildly
different messages depending on if Alt is pressed or not. The symbol
chosen now follows the standard behaviour on X11.