Fix KotlinTemplate stub generation for annotations on methods and variables

[MBoegers]

What's changed?

AnnotationTemplateGenerator hardcoded Java syntax for the dummy declarations that annotation template stubs attach to ( void $method() {} and int $variable;). This change extracts them into protected hooks — addDummyMethod(StringBuilder), addDummyVariable(StringBuilder), and the variable() helper — alongside the existing addDummyClass/addDummyAnnotationType hooks from #6522, and overrides them in KotlinAnnotationTemplateGenerator with Kotlin syntax.

What's your motivation?

Any KotlinTemplate applied with annotation coordinates (e.g. annotation.getCoordinates().replaceArguments()) on a method or property failed, because the generated stub mixed Java member syntax into a Kotlin source:

Could not parse as Java:
class Test{/*__TEMPLATE_cfcc2025-6662__*/@Example("RedundantSuppression")
 void $method() {}}
annotation class `$Placeholder` {}

Two subtleties beyond the plain syntax swap:

• Stub fragments are concatenated on a single line, and a return ...; is appended when the enclosing function declares a return type — so the Kotlin stubs need explicit ; terminators (val `$variable`: Int = 0;), otherwise a local val annotation inside fun foo(): Int produced the unparseable val `$variable`: Int = 0return null;.
• variable() (used to stub out locals that precede the templated annotation) emitted Java declaration order (Int y;); the Kotlin override emits val y: Int.

Base implementations keep byte-identical output, so Java and Groovy templates are unaffected.

Anything in particular you'd like reviewers to focus on?

• ScalaAnnotationTemplateGenerator has the same latent gap (it still inherits the Java method/variable stubs), left for a follow-up since rewrite-scala has no annotation-template test coverage yet.
• Test coverage spans the distinct stub-assembly paths: method in class, top-level function, property, class, local val (with enclosing return type, and preceded by a typed local), parameter substitution (#{any()}), and cursor-at-declaration via addAnnotation.

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Good to fix this generically, thanks!