Replace the Scala threading instrumenter with IntelliJ's TMH Java sources

[Vasil Vasilev (vasilmkd)]

Summary

This PR replaces the hand-written Scala port of the threading annotation instrumentation
(#SCL-18660) with the original Java sources from IntelliJ IDEA's JPS build, copied verbatim —
the same approach already used for the @NotNull instrumentation (#SCL-22085).

The Scala port (Feb 2, 2024) had drifted from upstream: three days after it was written,
IntelliJ's JPS switched to generating ThreadingAssertions calls
(IJPL-255) and chose softAssertReadAccess
for @RequiresReadLock, while our port generates the hard assertReadAccess. Copying the
upstream implementation removes this drift and the maintenance burden of keeping a parallel
port in sync.

⚠️ Behavior change

Matching IntelliJ IDEA's own instrumentation, @RequiresReadLock violations now log an
error instead of throwing an exception (ThreadingAssertions.softAssertReadAccess). This
may change what CI reports for read-lock issues in projects using
instrumentThreadingAnnotations := true. All other annotations still throw as before.

Implementation

• TMHInstrumenter, TMHAssertionGenerator, and TMHAssertionGenerator2 are copied
  verbatim from IntelliJ IDEA Community Edition (Apache 2.0, commit 7a35a7d7fe64 — the
  same commit the notNullVerification sources were copied from). The only changes are the
  package name, the ASM package, Opcodes.API_VERSION → Opcodes.ASM9, and the
  FailSafeMethodVisitor import (reusing the copy we already have).
  TMHAssertionGenerator1 (the legacy fallback for SDKs without ThreadingAssertions) is
  not copied — the previous implementation already required ThreadingAssertions, so
  nothing regresses.
• ThreadingAnnotationInstrumenter.scala shrinks from ~106 lines of ASM visitor logic to a
  thin wrapper around TMHInstrumenter. Same object name and signature, so
  ManipulateBytecode and the instrumentThreadingAnnotations setting are unchanged.
• org.jetbrains:annotations moves from Test to compile scope, since the copied sources use
  @ApiStatus.Internal/@NotNull.
• Minor behavior fix for free: methods opted out via generateAssertion = false no longer
  trigger a pointless no-op rewrite of their class file.

Tests

The fixture harness from NotNullInstrumenterTest is extracted into a shared
InstrumenterTestHarness trait, and a new ThreadingAnnotationInstrumenterTest (5 tests)
compiles stub com.intellij.util.concurrency classes at test runtime whose assertion
methods record their invocations. It pins the annotation → assertion mapping (including
@RequiresReadLock → softAssertReadAccess), assertion-before-body ordering, the
generateAssertion = false opt-out, no-op behavior on unannotated classes, and the
one-assertion-per-method behavior for doubly-annotated methods (which matches upstream's
last-annotation-wins semantics).