Highlighting does not work on large PRs

[aidando73]

[aidando73]

MutationObserver does not fire on file-content (on childList and subtree - probably due to how the shadow dom works).

But it does fire on attributes (on aria-label)

const allDiffsObserver = new MutationObserver((mutations) => {
  mutations
    .forEach(mutation => {
      if (mutation.type === 'attributes' && mutation.attributeName === 'aria-label') {
        highlightDiffFile(mutation.target);
      }
    });
});

E.g., the above mostly works. This works with both the arrows and individual files (but doesn't when a picture is previous photo).

One solution is to check whether the PR is a large one (e.g. search for "This is a large PR.") and then behave differently.

This also could be the more maintainable approach as the two styles behave quite differently and it'd be easier to find solutions when they're separate instead of bundled into one.