java/bouncycastle15: Make sure we don't miss jars with future updates

The do-install-* targets will now automatically install all the
relevant files provided by the port.

Also while here:

• Replace PORTDOCS with pkg-plist entries for greater control over the docs.
• Move ZIPSRC-only install targets to ZIPSRC_ALL_TARGET.
• Sort pkg-plist.
• Add a comment explaining why the port installs the bundled version of bcprov.jar.
• Install additional documentation (docs and tls/docs).

Sponsored by: Modirum MDPay
Sponsored by: Klara, Inc.