Refine highlighting of '@'

- Do not highlight '@' as separate token.

- Highlight '@' the same way as element where it's located: annotation, label or modifier.

- Extend text range when positioning unresolved reference in annotation with '@'.

Note that currently '@' is collapsed with modifiers tokens

compiler/testData/diagnostics/tests/annotations/unresolvedReferenceRange.kt

@@ -0,0 +1,3 @@
+<!UNRESOLVED_REFERENCE!>@Ann<!> class A
+<!UNRESOLVED_REFERENCE!>Ann<!> class B
+<!UNRESOLVED_REFERENCE!>@Ann<!>(1) class C