Upgrade to JDK 22

[msgilligan]

This PR will resolve Issue #6 and Issue #9

• Use Java Toolchains to use JDK 22 for compile/test
• Remove --enable-preview
• Use JDK 21 for -api and -bouncy modules (we're using a JDK 21 feature in API currently, we need to backport this to en earlier JDK version)
• Use JDK 21 temporarily for Kotlin examples (until Kotlin supports JDK 22)
• Use BouncySecp256k1 in the Kotlin examples (which means they won't run until Bouncy is finished) but they will at least compile.
• Update the extract-headers.sh script to work with JDK 22 and the latest jextract
• Update OpaqueKeyPair and Secp256k1Foreign to use the JDK 22 FFM API
• Replace the o.b.s.f.jextract Java files with the files generated by the latest jextract.

This is WIP because the GitHub Actions build needs an update.

[schildbach]

I think if this PR is WIP it might be a good idea to use the GitHub "Draft" feature.

[msgilligan]

I think if this PR is WIP it might be a good idea to use the GitHub "Draft" feature.

We can't use it in a private repo without paying 😕

[msgilligan]

Approved. I only wonder why the jextract is under version control if it's generated as you say.

I think the recommend use of jextract is to get your initial implementation quickly, but then to customize it and maintain it manually. I think that is the path we will pursue. (If not, we can change things to run jextract as part of the build.)