Instrument @NotNull assertions into the compiled JVM bytecode #SCL-22085

[Vasil Vasilev (vasilmkd)]

Supersedes #150.

Summary

This PR adds @NotNull/@Nullable bytecode instrumentation, expanding the annotation
instrumentation feature introduced with the threading annotations (#SCL-18660). It provides
feature parity with IntelliJ's internal JPS build and the IntelliJ Platform Gradle Plugin's
instrumentCode task.

Two new settings control the feature:

• instrumentNotNullAnnotations: SettingKey[Boolean] (default: false) — generates null
  checks for annotated method parameters (throwing IllegalArgumentException) and return
  values (throwing IllegalStateException), with the same bytecode and error messages as
  IntelliJ's own build.
• notNullAnnotations: SettingKey[Seq[String]] (default:
  Seq("org.jetbrains.annotations.NotNull")) — the annotation classes to instrument.

Implementation

• The instrumenter core (NotNullVerifyingInstrumenter, AuxiliaryMethodGenerator,
  FailSafeClassReader, FailSafeMethodVisitor) is copied verbatim from IntelliJ IDEA
  Community Edition (Apache 2.0, commit 7a35a7d7fe64). The only changes are the package
  name, the ASM package (org.jetbrains.org.objectweb.asm → org.objectweb.asm), and
  Opcodes.API_VERSION → Opcodes.ASM9, keeping the sources easy to diff against upstream.
  No Ant machinery is needed — the Gradle plugin's "Ant task" is a wrapper around this
  same class, which we call directly.
• A small Scala wrapper (NotNullInstrumenter) handles what JPS's builder infrastructure
  does there: COMPUTE_FRAMES writer flags with common-superclass resolution against the
  project classpath (classDirectory + dependencyClasspath), plus the module-info and
  class-file-version gates.
• Wired into the existing manipulateBytecode flow next to the threading instrumentation;
  both instrumenters share the changed-classes detection and zinc re-stamping.
• Kotlin classes (kotlinc emits its own assertions), bridge methods, and provably non-null
  returns are skipped, as upstream does.

Tests

New NotNullInstrumenterTest (9 tests, modeled on IDEA's NotNullVerifyingInstrumenterTest):
fixtures are compiled with javax.tools at test runtime, instrumented, then loaded and
invoked in a throwaway classloader — covering parameter/return checks, parameter names from
debug info, custom messages, custom annotations with custom exception classes, enum and
inner-class constructor parameter offsets, the non-null peephole, and the Kotlin skip.

Housekeeping

Also included as separate commits:

• sbt 1.12.14 (project + CI runner), sbt-ci-release 1.12.0
• Scala 2.12.21
• Library updates: scalatest 3.2.20, circe 0.14.16, httpclient5 5.6.2,
  marketplace-zip-signer 0.1.43, asm 9.10.1, commons-io 2.22.0, annotations 26.1.0
• actions/checkout@v7