Apply format only if --format is specified (#79466)

clang-apply-replacements used to apply format even without --format is
specified. This because, methods like createReplacementsForHeaders only
takes the Spec.Style and would re-order the headers even when it was not
requested. The fix is to set up Spec.Style only if --format is provided.

Also added note to ReleaseNotes.rst

Based on https://github.com/llvm/llvm-project/pull/70801



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Co-authored-by: Kugan <34810920+kuganv@users.noreply.github.com>
Co-authored-by: Aaron Ballman <aaron@aaronballman.com>