[Repo Assist] Fix trailing comments in record types not indented to field level

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Closes #2482

Root Cause

In genRecordFields, the ContentBefore trivia of the closing brace (}) — which contains commented-out lines appearing after the last field — was written via genSingleTextNode node.ClosingBrace after the unindent that ends the field block. This caused comments to be written at the brace-level indent (e.g., column 4) rather than the field-level indent (e.g., column 8).

For example, with aligned brackets:

// Before fix:
type UserInfo =
    {
        UserId: int
    // Roles: Role list   ← was at column 4 (wrong)
    }

Fix

enterNode closingBrace (which emits ContentBefore) is now called inside the indent block, before unindent, so comments are written at field-level indent.

One subtlety: when CommentOnSingleLine trivia is emitted, its trailing sepNlnForTrivia pre-commits a new blank line in the WriterModel with the current (field-level) indent. After unindent, we detect this pre-committed blank line and replace it with the correct (brace-level) indentation — ensuring the closing brace lands at the right column.

The closing brace text is then written using recordCursorNode + leaveNode directly, skipping enterNode to avoid re-emitting ContentBefore.

Result

// After fix (aligned):
type UserInfo =
    {
        UserId: int
        // Roles: Role list   ← now at column 8 ✓
    }

// After fix (Stroustrup):
type UserInfo = {
    UserId: int
    // Roles: Role list   ← now at column 4 ✓
}

This affects the Aligned and Stroustrup MultilineBracketStyle modes. The Cramped mode uses a separate code path and is not changed.

Trade-offs

• The fix involves a targeted direct mutation of WriterModel.Lines to correct the pre-committed indentation. This is intentional: the WriterEvents queue is a diagnostic side channel; the authoritative output state is WriterModel.Lines.
• The correction only fires when the head of Lines is a blank (whitespace-only) line, so it cannot accidentally affect records without trailing comments.

Test Status

• ✅ Build succeeded (0 warnings, 0 errors)
• ✅ All 2741 tests pass (2 new tests added for this fix: one for aligned style, one for Stroustrup style)

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[nojaf]

Horrible