Explore using toolchain to run tests on versions of Java prior to 17 while running Gradle 9 with Java 17

[cherylking]

When adding support for Gradle 9, the minimum JVM for running Gradle is Java 17. See this issue for more details.

An important distinction was made in that issue that tests can still run with Java 8. We need to explore toolchain to enable running Gradle with supported LTS releases (17 and 21 today, 25 at a later date) while running the tests at all supported LTS releases (8, 11, 17, 21).

[cherylking]

Actually according to this document, maybe toolchains are not supported on Java 8 and 11. Still need to figure out how to run tests with Java 8 and 11 while running Gradle with Java 17 and 21.

I neglected to include a link to the document before. Here is some doc on toolchains.

[cherylking]

I think we would need to do something like this to make multiple versions of Java available. We would want to build the plugin and run Gradle with Java 17 and 21, but build and run tests with Java 8, 11, 17 and 21.