BouncyCastle supports reading GPG keys without passphrase since 1.62.
Handle this in JGit, too, and don't prompt for a passphrase unless
it's necessary.

Make two passes over the private key files, a first pass without
passphrase provider. If that succeeds it has managed to read a
matching key without passphrase. Otherwise, ask the user for
the passphrase and make a second pass over the key files.

BouncyCastle 1.65 still has no method to get the GPG "key grip" from
a given public key, so JGit still cannot determine the correct file
to read up front. (The file name is the key grip as 40 hex digits,
upper case, with extension ".key").

Bug: 548763
Change-Id: I448181276548c08716d913c7ba1b4bc64c62f952
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Motivation: BouncyCastle serves as 'default' implementation of
the GPG Signer. If a client application does not use it there is no need
to pull in this dependency, especially since BouncyCastle is a large
library.

Move the classes depending on BouncyCastle to an OSGi fragment extending
the org.eclipse.jgit bundle. They are moved to a distinct internal
package in order to avoid split packages. This doesn't break public API
since these classes were already in an internal package before this
change.

Add a new feature org.eclipse.jgit.gpg.bc to enable installation. With
that users can now decide if they want to install it.

Attempts to sign a commit if org.eclipse.jgit.gpg.bc isn't available
will result in ServiceUnavailableException being thrown.

Bug: 559106
Change-Id: I42fd6c00002e17aa9a7be96ae434b538ea86ccf8
Also-by: Michael Dardis <git@md-5.net>
Signed-off-by: Michael Dardis <git@md-5.net>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Signed-off-by: David Ostrovsky <david@ostrovsky.org>

This is the format given by the Eclipse legal doc generator [1].

[1] https://www.eclipse.org/projects/tools/documentation.php?id=technology.jgit

Bug: 548298
Change-Id: I8d8cabc998ba1b083e3f0906a8d558d391ffb6c4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

This also includes a change to generating the jgit CLI jar. Shading is
no longer possible because it breaks the signature of BouncyCastle.
Instead, the Spring Boot Loader Maven plug-in is now used to generate an
executable jar.

Bug: 382212
Change-Id: I35ee3d4b06d9d479475ab2e51b29bed49661bbdc
Also-by: Gunnar Wagenknecht <gunnar@wagenknecht.org>
Signed-off-by: Gunnar Wagenknecht <gunnar@wagenknecht.org>
Signed-off-by: Medha Bhargav Prabhala <mprabhala@salesforce.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>