Show clang-tidy fixes that could not be applied in the PR comment and review summary #490

Follow-up to #475 / #488, requested by @2bndy5 in #488 (comment). It should be done before the next RC release.

Current behavior (after #488)

When a clang-tidy fix touches a file other than the analyzed one, cpp-linter doesn't apply it. It only writes an info-level log line, which users rarely see. In the thread comment and the PR review, the diagnostic looks like any other, and nothing says part of its fix was left out.

Proposal

• Record the not-applied fixes on the TidyNotification (or TidyAdvice), e.g. the other file's path and why the fix was skipped (outside the analyzed files, outside the changed lines).
• Mention them in make_tidy_comment() and in the review summary, so users know to apply that part themselves (for example, the header declaration that needs the same const).
• Apply clang-tidy fixes to other analyzed files after all files are analyzed #489 (applying fixes to other analyzed files) will reduce the cases this has to report, so it may be easier to do this after Apply clang-tidy fixes to other analyzed files after all files are analyzed #489.