[FIR] Rename PLUGIN_ANNOTATION_AMBIGUITY to COMPILER_REQUIRED_ANNOTATION_AMBIGUITY

This diagnostic may be reported even without any compiler plugins (e.g.
  for annotation named `Target` or `Deprecated`), so the old name
  and message were quite confusing

^KT-64654

compiler/testData/diagnostics/testsWithStdLib/annotations/annotationTargetResolvedAmbiguously.fir.kt

@@ -36,7 +36,7 @@ abstract class Base {
 }
 
 class Derived : Base() {
-    @<!PLUGIN_ANNOTATION_AMBIGUITY!>Target<!>(<!ARGUMENT_TYPE_MISMATCH!>AnnotationTarget.<!AMBIGUOUS_ANNOTATION_ARGUMENT!>TYPE<!><!>)
+    @<!COMPILER_REQUIRED_ANNOTATION_AMBIGUITY!>Target<!>(<!ARGUMENT_TYPE_MISMATCH!>AnnotationTarget.<!AMBIGUOUS_ANNOTATION_ARGUMENT!>TYPE<!><!>)
     annotation class Ann
 
     fun foo(x: <!WRONG_ANNOTATION_TARGET!>@Ann<!> String) {}