…keep-attributes-with-mustache-placeholders-intact

* 'develop' of github.com:ampproject/amp-wp: (113 commits)
  This converts the keyboard cut handler to equal a copy handler to avoid bugs
  Fix aria-label adding helper function
  Remove extra line I added in resolving merge conflict
  Fix alignment of arrow
  Fix custom CTA text for page attachment
  Fix cut handler by shortcut
  Cleanup of duplicated comment
  Add unit testing to `addVideoAriaLabel`
  Remove unused piece of code
  Remove Cloudflare AMP cache since deprecated
  Handle cut keyboard requests. (#3231)
  Page Attachment block (#3035)
  Keyboard & Right-Click Menu Copy + Paste (#3083)
  Animation Previews (#3104)
  Make internal methods inaccessible
  Omit the ecosystem link also when using a core theme
  Add skipped e2e test for the video block
  Add array_colum() pollyfill for PHP < 5.5
  Add asserts to make sure we are not enqueueing both versions of dashicons
  Remove useless variable
  ...