Upgrade to GraalVM JDK 21.
```
> java -version
openjdk version "21" 2023-09-19
OpenJDK Runtime Environment GraalVM CE 21+35.1 (build 21+35-jvmci-23.1-b15)
OpenJDK 64-Bit Server VM GraalVM CE 21+35.1 (build 21+35-jvmci-23.1-b15, mixed mode, sharing)
```
With SDKMan, download with `sdk install java 21-graalce`.
# Important Notes
- After this PR, one can theoretically run enso with any JRE with version at least 21.
- Removed `sbt bootstrap` hack and all the other build time related hacks related to the handling of GraalVM distribution.
- `project-manager` remains backward compatible - it can open older engines with runtimes. New engines now do no longer require a separate runtime to be downloaded.
- sbt does not support compilation of `module-info.java` files in mixed projects - https://github.com/sbt/sbt/issues/3368
- Which means that we can have `module-info.java` files only for Java-only projects.
- Anyway, we need just a single `module-info.class` in the resulting `runtime.jar` fat jar.
- `runtime.jar` is assembled in `runtime-with-instruments` with a custom merge strategy (`sbt-assembly` plugin). Caching is disabled for custom merge strategies, which means that re-assembly of `runtime.jar` will be more frequent.
- Engine distribution contains multiple JAR archives (modules) in `component` directory, along with `runner/runner.jar` that is hidden inside a nested directory.
- The new entry point to the engine runner is [EngineRunnerBootLoader](https://github.com/enso-org/enso/pull/7991/files#diff-9ab172d0566c18456472aeb95c4345f47e2db3965e77e29c11694d3a9333a2aa) that contains a custom ClassLoader - to make sure that everything that does not have to be loaded from a module is loaded from `runner.jar`, which is not a module.
- The new command line for launching the engine runner is in [distribution/bin/enso](https://github.com/enso-org/enso/pull/7991/files#diff-0b66983403b2c329febc7381cd23d45871d4d555ce98dd040d4d1e879c8f3725)
- [Newest version of Frgaal](https://repo1.maven.org/maven2/org/frgaal/compiler/20.0.1/) (20.0.1) does not recognize `--source 21` option, only `--source 20`.
New plan to [fix the `sbt` build](https://www.pivotaltracker.com/n/projects/2539304/stories/182209126) and its annoying:
```
log.error(
"Truffle Instrumentation is not up to date, " +
"which will lead to runtime errors\n" +
"Fixes have been applied to ensure consistent Instrumentation state, " +
"but compilation has to be triggered again.\n" +
"Please re-run the previous command.\n" +
"(If this for some reason fails, " +
s"please do a clean build of the $projectName project)"
)
```
When it is hard to fix `sbt` incremental compilation, let's restructure our project sources so that each `@TruffleInstrument` and `@TruffleLanguage` registration is in individual compilation unit. Each such unit is either going to be compiled or not going to be compiled as a batch - that will eliminate the `sbt` incremental compilation issues without addressing them in `sbt` itself.
fa2cf6a33ec4a5b2e3370e1b22c2b5f712286a75 is the first step - it introduces `IdExecutionService` and moves all the `IdExecutionInstrument` API up to that interface. The rest of the `runtime` project then depends only on `IdExecutionService`. Such refactoring allows us to move the `IdExecutionInstrument` out of `runtime` project into independent compilation unit.
