Add RemoveDuplicateAnnotations

[timtebeek]

• Extracted from Do not duplicate JSpecify annotations when several annotations map to one rewrite-migrate-java#1200, where this started life as a JSpecify-specific recipe before we realised it applies far more widely.

When several distinct annotations migrate to a single new annotation, each ChangeType rewrites its own annotation and the element ends up annotated twice:

import javax.annotation.CheckForNull;
import javax.annotation.Nullable;

class Foo {
    public void bar(@Nullable @CheckForNull String baz) {
    }
}

• becomes @Nullable @Nullable String baz — sometimes with one of the two fully qualified, when the simple name can no longer be shortened. That is a compile error for non-@Repeatable annotations. See JSpecifyBestPractices add @Nullable annotionen to params twice rewrite-migrate-java#1199 for a report in the wild.

This recipe removes annotations repeated on the same element, keeping the first occurrence. It covers leading annotations on classes, methods and variables, annotations attached to modifiers, and type-use annotations on array types, nested types and type arguments.

Two guards keep it conservative:

• only annotations semantically equal to an earlier one are removed, so @Nullable @NonNull and @Tag("a") @Tag("b") are untouched;
• @Repeatable annotations are skipped, since repeating those is meaningful.

annotationType is optional and defaults to any annotation, so the recipe is useful standalone; rewrite-migrate-java will call it with org.jspecify.annotations.* from its JSpecify migrations.

[timtebeek]

CI is red on ten TypeScript tests (JSON-RPC peer closed the stream / RPC process shut down early with exit code 1). Those are pre-existing on main — the same ten fail in run 31728116299 on main at 17:55, before this branch, and they fail locally on a clean checkout too. RemoveDuplicateAnnotationsTest passes.