Figure out how to update Eclipse version dependence

[msridhar]

Figure out how to update Eclipse version dependence

[liblit]

perhaps there is a way to only require JDK 17 if you want to run the ECJ front end.

This feels quite doable. We would need to use JDK 17 in just the Gradle submodules that call into JDK 17+ Eclipse code. All Eclipse-independent code can still use JDK 11.

To start, try adding the following to build.gradle.kts in each subdirectory that calls into ECJ:

java.toolchain.languageVersion = JavaLanguageVersion.of(17)

It's also possible that the right place for this configuration tweak is somewhere in eclipse-maven-central.gradle.kts, since that seems to be the place where the current version 4.21.0 is put to use. But I'd probably start by tweaking just one or two specific */build.gradle.kts files, then retroactively deciding whether the */build.gradle.kts files that needed to be changed are exactly the ones that use eclipse-maven-central.gradle.kts.

I cannot guarantee that this is all we need to do, but it's a good start.

[liblit]

I'm going to noodle around with this for a bit and see how far I get.