Update JDK/JRE + Gradle

[skovati]

• Tickets addressed: closes Upgrade to JRE 21 #1209
• Review: By commit
• Merge strategy: Merge (no squash)

Description

Updates JDK/JRE to 21, as well as Gradle to 8.4 8.6.

Updates sim engine to only use virtual thread per-task executor. Removes a test that checks thread count in the sim driver since that fails with virtual threads. @Twisol

Verification

Just 👀'ing at e2e-tests

Future work

A few TODOs are now unblocked by this JDK update. (e.g. rg "TODO" | rg "21")

[skovati]

Manual testing has shown:

• JDK 19 built models run fine on Aerie w/ JRE 19
• JDK 19 built models run fine on Aerie w/ JRE 21
• JDK 21 built models DO NOT run on Aerie w/ JRE 19
• JDK 21 built models run fine on Aerie w/ JRE 21

So, upgrading the JRE of aerie-* container images should be backwards compatible, but mission modelers will need to hold off on upgrading to JDK 21 until their target venues are also running JRE 21.

[camargo]

We should also update https://github.com/NASA-AMMOS/aerie-mission-model-template as well :)

[dandelany]

Reviewers of this PR should:

• checkout the PR
• try to build Aerie on your local machine
• see if you run into any issues with gradle trying to automatically update the toolchain
• document any additional steps needed to get it working

[dandelany]

Pending a couple questions that @skovati will look into:

• Can/should we replace the thread release test with something new supported by Loom?
• Can we upgrade to latest gradle (now >8.4)

[dandelany]

@Mythicaeda will test this with building the Clipper model in JDK 21

[Mythicaeda]

I've tested building the Clipper model against this branch. Once I was able to get the Clipper model to accept Java 21 artifacts, it compiled on J21 and simulated, although I do not do a deep dive into whether the results were the same as the version compiled on J19 using J19 Aerie artifacts (I did check a couple views, though, and didn't see any differences).

However, in order to get Clipper to build I had to change the Clipper build process, as they specifically look for Java 19 artifacts and reject JARs compiled on other Java versions. This means that the version of Aerie that includes the J21 upgrade will be breaking to Clipper.

Details for how to update Clipper model to support JDK 21:

• Update Grade wrapper to one that supports J21 (I chose 8.6)
• Update the Java sourceCompatibilty/targetCompatability statements in gov.nasa.jpl.europa.clipper.aerie.adaptations.java-common-conventions.gradle (I chose to remove these for the sake of getting a build working, but a more delicate change should work)

[Mythicaeda]

I've tested locally and it LGTM!

[dandelany]

Merging to include with 2.4.0 release - thanks!