Fix duplicated comments in for..of formatter

[cknitt]

Summary

Fixes #8394.

• Fix comment attachment for for..of and for await..of loops.
• Add formatter regression coverage for comments in both loop forms.
• Confirm range for and while loops are not affected by the issue.

Details

Issue #8394 was caused by the comment walker for Pexp_for_of and
Pexp_for_await_of passing the same full comment list to the loop pattern,
iterable expression, and body. That allowed a single source comment to attach to
multiple nodes, so formatting duplicated it and repeated formatting compounded
the duplication.

The fix partitions comments through the pattern, iterable expression, and body,
matching the ownership approach already used by normal range for loops.

Verification

• Reproduced the original duplication locally before the fix.

• Checked for..of, for await..of, range for, and while with body
  comments after the fix.

• Ran targeted printer fixture diff:

  _build/install/default/bin/res_parser tests/syntax_tests/data/printer/comments/expr.res > /tmp/expr8394.out
  diff -u tests/syntax_tests/data/printer/comments/expected/expr.res.txt /tmp/expr8394.out

• Ran a two-pass formatter roundtrip for the reproducer.

• Ran make checkformat.

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commit: 9368d41