Fix Scala parser losing type attribution when classpath lacks stdlib

[knutwannheden]

Motivation

mod build on openrewrite/rewrite fails to type-check 5 Scala files that import dotty compiler APIs, emitting errors such as:

Bad symbolic reference. A signature in scala3-compiler_3-3.8.4-RC2.jar(dotty/tools/dotc/core/Contexts.tasty)
refers to */T in object dotty.tools.dotc.core.Contexts which is not available.

Root cause: when a caller's classpath includes scala3-compiler but is missing one of the stdlib jars dotty relies on (scala-library, tasty-core), dotty's Definitions can't resolve foundational types like scala.Unit. Depending on where typechecking blows up, this surfaces as the Bad symbolic reference TASTy error above, or as a ClassCastException: NoSymbol cannot be cast to ClassSymbol in Definitions.UnitClass. Either way, the affected files lose type attribution entirely.

Because ScalaCompilerBridge itself is loaded from those same jars, it can locate them at runtime and self-heal — analogous to how JavaParser doesn't require callers to pass rt.jar.

Summary

• ScalaCompilerBridge now computes the dotty classpath through a new buildClasspath helper that appends any missing stdlib jars (scala-library, tasty-core, scala3-compiler), located via ProtectionDomain.getCodeSource() on probe classes (scala.Option, dotty.tools.tasty.TastyFormat, dotty.tools.dotc.core.Contexts).
• The self-heal only triggers when the caller's classpath already contains at least one scala*/tasty*/dotty* artifact. This preserves the narrow-classpath contract that ScalaTemplate depends on to keep type resolution out of template parsing.
• Dedup is filename-based so callers that pass the same artifact under a different on-disk path (Maven vs. Gradle cache, symlinks) don't end up with duplicate entries.
• New regression test DottyImportTypeAttributionTest feeds the bridge a classpath containing only scala3-compiler (mimicking the mod build scenario) and verifies that both an ordinary Scala file and one importing dotty.tools.dotc.core.Contexts.* come back with a populated typed tree.
• Drive-by: drop :latest.release from three junit-jupiter test dependencies in rewrite-scala/build.gradle.kts. :latest.release was resolving to 6.1.0-M1 (milestone), whose junit-platform-commons removed CollectionUtils.toUnmodifiableList() — breaking the junit-platform-launcher:1.14.0 that Gradle's test runner uses. No tests in this module could run. Inheriting from the junit BOM (as the other modules do) restores consistency.

Test plan

• ./gradlew :rewrite-scala:test — full module green, including the new DottyImportTypeAttributionTest and the pre-existing template/matching suites.
• Manual mod build on a fresh openrewrite/rewrite checkout with the CLI's sibling-Java fix (moderneinc/moderne-cli#3704) to confirm the Bad symbolic reference errors no longer appear on the 5 files listed in the motivation.