Components: Extract a reusable PostLastRevision component

[youknowriad]

Related to #2761 (comment)

All these (the sidebar panels) must be refactored slightly to drop all the "layout" pieces and keep only the "forms". For example, the sidebar panels like PostTaxonomies, we should extract only the PostTaxonomyForms into a reusable component without the expandable panel behavior that is specific to our current UI. (This step could be done in a separate PR preceding the directory structure change)

This PR addresses the comment above for the PostLastRevision component.

Testing instructions

• Test that the last revision link is working as expected

[codecov]

Codecov Report

Merging #3290 into master will decrease coverage by 0.06%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #3290      +/-   ##
==========================================
- Coverage   31.05%   30.98%   -0.07%     
==========================================
  Files         232      234       +2     
  Lines        6521     6535      +14     
  Branches     1163     1165       +2     
==========================================
  Hits         2025     2025              
- Misses       3770     3782      +12     
- Partials      726      728       +2

Impacted Files	Coverage Δ
editor/sidebar/last-revision/index.js	0% <0%> (ø)	⬆️
editor/post-last-revision/index.js	0% <0%> (ø)
editor/post-last-revision/check.js	0% <0%> (ø)

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[gziolo]

Nice one 👍