Fix Kotlin parser handling of unresolved callable references

[knutwannheden]

Motivation

Parsing the buildSrc/build.gradle.kts file from the google/dagger repo fails with a print idempotency error:

java.lang.IllegalStateException: buildSrc/build.gradle.kts is not print idempotent.
diff --git a/buildSrc/build.gradle.kts b/buildSrc/build.gradle.kts
@@ -28,3 +28,4 @@
 lint {
   baseline = file("lint-baseline.xml")
 }
+

The root cause is KotlinTreeParserVisitor#visitCallableReferenceExpression. It was checking the FIR mapping of the callable reference's right-hand-side name (expression.getCallableReference()). When the receiver type is unresolved — e.g. JavaLanguageVersion::of in a .gradle.kts parsed without the full Gradle classpath — the RHS maps to FirErrorNamedReferenceImpl, even though the whole expression still maps cleanly to FirCallableReferenceAccess. The visitor threw, the whole KtScript declaration bubbled up into J.Unknown, and the J.Unknown PSI text range (which included the trailing \n) then got duplicated against the file-level EOF space — producing the extra blank line on print.

Summary

• KotlinTreeParserVisitor#visitCallableReferenceExpression now validates the expression-level FIR (FirCallableReferenceAccess) rather than the RHS-name FIR, and uses the RHS FIR only for optional type resolution; types remain null when the reference is unresolved, consistent with other unresolved-type paths.
• Re-enables the previously @Disabled MemberReferenceTest#firCallableReferenceAccess regression test.
• Adds CompilationUnitTest#unresolvedCallableReference (.kts path) and GradleParserTest#kotlinDslWithUnresolvedCallableReference (Gradle entry point) covering the reproduction.

Test plan

• MemberReferenceTest#firCallableReferenceAccess (re-enabled) passes
• New CompilationUnitTest#unresolvedCallableReference passes
• New GradleParserTest#kotlinDslWithUnresolvedCallableReference passes
• Full rewrite-kotlin test suite passes
• Full rewrite-gradle test suite passes