Add GraalVM for JDK 21 support.

[kkriske]

• no longer register HomeFinderFeature post JDK 21
• no longer link against fdlibm on Windows and Linux post JDK 21
• link against extnet and mswsock on Windows post JDK 21
• add --add-exports flag required for the GluonFeature internal API usage

Issue

Builds against GraalVM for JDK 21 run into some issues:

• The HomeFinderFeature is no longer available by default since it's part of polyglot, and polyglot has been split off to separate maven artifacts. The feature is also automatically registered in a native-image.properties file in the META-INF of that dependency so it should not be required to register it manually.

Windows specific issues:

• the nio library now depends on mswsock, so that needs to be added to the linker
• the fdlibm library is no longer part of the JDK so it should be removed from the linker, not sure since what exact JDK version
• the extnet library is now used on Windows in the WindowsSocketOptions class, so it needs to be added to the linker

Linux specific issues:

• the fdlibm library is no longer part of the JDK so it should be removed from the linker, not sure since what exact JDK version

Other:

• fdlibm should probably be removed from the remaining targets as well, but I have no way to verify that.

Progress

• [ ] Change must not contain extraneous whitespace
• [ ] License header year is updated, if required
• [x] Verify the contributor has signed Gluon Individual Contributor License Agreement (CLA)

[jperedadnr]

@kkriske please fix conflicts (and do the refactoring if needed)

[credmond]

I've left some comments. Tested successfully (with some changes) on Mac with Gluon's GraalVM 22.1.0.1-Final and the official GraalVM 21+35.1 (using also #1234)

In any case, note that the official GraalVM 21 builds will still fail building native images for mobile targets (more changes are required on Substrate, but also probably on the GraalVM builds)

Hey...could you tell me if Gluon is planning on a new official Gluon GraalVM build anytime soon?