Components: Extract Reusable DocumentOutlineCheck component

[youknowriad]

Extract a reusable DocumentOutlineCheck component to the editor/components folder.
Needed to be able to separate the edit-post and editor module

Expect some similar PRs today, I'm going to merge them as soon as the tests pass, they consist of moving some files around.

Testing instructions

• Click the documnet outline panel shows up when you have two headings at least.

[codecov]

Codecov Report

Merging #3645 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #3645      +/-   ##
==========================================
- Coverage    36.9%   36.88%   -0.02%     
==========================================
  Files         272      273       +1     
  Lines        6631     6634       +3     
  Branches     1201     1201              
==========================================
  Hits         2447     2447              
- Misses       3532     3535       +3     
  Partials      652      652

Impacted Files	Coverage Δ
editor/components/document-outline/check.js	0% <0%> (ø)
.../edit-post/sidebar/document-outline-panel/index.js	0% <0%> (ø)	⬆️

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