refactor(build): Make Document.findAll() asynchronous

[queengooborg]

This changes the findAll() function to an asynchronous function to help improve performance.

[caugner]

@queengooborg Something's not right here:

FAIL testing/tests/destructive.test.ts (8.328 s)
  ● fixing flaws › can be run in dry-run mode

    expect(received).toContain(expected) // indexOf

    Expected substring: "web/fixable_flaws/bad_pre_tags"
    Received string:    "Would modify \"/tmp/b7c3ee96e90472f73dd8e093d510da2d/content/files/en-us/web/fixable_flaws/index.html\" from fixable flaws."

      100 |       .filter((line) => regexPattern.test(line));
      101 |     expect(dryRunNotices).toHaveLength(4);
    > 102 |     expect(dryRunNotices[0]).toContain(path.join(pattern, "bad_pre_tags"));
          |                              ^
      103 |     expect(dryRunNotices[1]).toContain(path.join(pattern, "deprecated_macros"));
      104 |     expect(dryRunNotices[2]).toContain(path.join(pattern, "images"));
      105 |     expect(dryRunNotices[3]).toContain(pattern);

      at Object.toContain (tests/destructive.test.ts:102:30)

[queengooborg]

Odd that going async changed the order up, but it's now in an order I would expect anyways (and seems to be consistent as well), so a quick fix of the test did the trick!

[caugner]

LGTM, tested locally.