RFR: 8332474: Tighten up ToolBox' JavacTask to not silently access javac crash as a failure

[Jan Lahoda]

Tests for javac use several test frameworks, and one of them is the "toolbox", which provides `JavacTask` that allows to conveniently run javac on a given set of sources. The problem with `JavacTask` is that, by default, when a compilation failure is expected, javac crash (exit code 4) is tolerated by the `JavacTask`. And the test must manually select a specific exit code to overwrite this behavior.

This then leads to bugs like [https://bugs.openjdk.org/browse/JDK-8335385], which are silently ignored by `JavacTask`.

The proposal herein is to tighten up the `JavacTask`, and effectively disallow exit code 4 for `JavacTask` (but permit any other exit code, as javac is using several exit codes). The base implements in `AbstractTask` is changed to use a validator for the exit codes, which is then leveraged by `JavacTask`.

This patch depends on PR #19969, as that fixes JDK-8335385, where the javac crash is ignored. It also tweaks module attribution to not leave empty `JCModuleDecl.sym` for duplicate modules, and set it to an erroneous module. The empty (`null`) symbol here crashes javac in the `test/langtools/tools/javac/modules/MultiModuleModeTest.java#testDuplicateModules`, and the test wouldn't pass with this more strict `JavacTask`.

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Depends on: https://git.openjdk.org/jdk/pull/19969

Commit messages:
 - Fixing expect semantics
 - Cleanup.
 - Cleanup.
 - Merge branch 'JDK-8335385' into JDK-8332474
 - 8332474: Tighten up ToolBox' JavacTask to not silently access javac crash as a failure

Changes: https://git.openjdk.org/jdk/pull/19972/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19972&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332474
  Stats: 73 lines in 3 files changed: 64 ins; 1 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/19972.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19972/head:pull/19972

PR: https://git.openjdk.org/jdk/pull/19972