[Repo Assist] Fix block comment after 'of' in union cases and exceptions

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Closes #1959

Problem

Block comments positioned between of and the first field type in union cases and exception types were incorrectly moved before of in the formatted output.

Input:

exception LoadedSourceNotFoundIgnoring of (*filename*) string * range
type T = | Foo of (*label*) int * string

Before (buggy):

exception LoadedSourceNotFoundIgnoring (*filename*) of string * range
type T = Foo of (*label*) int * string  // comment was lost to before 'of'

After (fixed):

exception LoadedSourceNotFoundIgnoring of (*filename*) string * range
type T = Foo of (*label*) int * string

Root Cause

In blockCommentToTriviaInstruction (Trivia.fs), when the comment sits on the same line as nodeBefore (the union case identifier), the logic unconditionally called nb.AddAfter — attaching the comment after the identifier. However, the of keyword is implicit (not a separate AST node), so this placed the comment before of in the output.

Fix

Added a special case: when the container is a UnionCaseNode and nodeBefore is the identifier (SingleTextNode), use na.AddBefore (attach before the first FieldNode) instead of nb.AddAfter. This correctly places the comment after the implicit of.

The fix is guarded so it only applies to this specific scenario — comments between fields (where nodeBefore is an IdentListNode, not a SingleTextNode) are unaffected.

Tests

• Added block comment between 'of' and field type in exception stays after 'of', 1959
• Added block comment between 'of' and field type in union case stays after 'of', 1959
• Updated block comments in type definition, 1975 — this test was documenting the old buggy behaviour; corrected expected output
• All 2739 tests pass, 7 skipped

Test Status

✅ Build succeeded
✅ All 2739 tests pass (0 failures, 7 skipped)

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[nojaf]

/repo-assist the real fix here is having the off keyword as trivia on the parser side.