Remove Largo's pseudoelement lines at top and bottom of pull quotes; replace with actual borders so that Gutenberg's pull quote "primary color" selector works.

[benlk]

In be30571 in #1746, as a quick fix for the issue where Gutenberg's editor styles provided thick 4px borders top and bottom to pull quotes that duplicated Largo's built-in borders top and bottom, I hid Gutenberg's borders in the editor.

They were already hidden in the frontend; this bug is not new in #1746. All #1746 did was hide the Gutenberg-provided, Gutenberg-styled borders in the editor.

However, those borders are the elements that get colored by the inline border-color styles set by the "Main Color" control on the pull quote block.

Steps to fix:

• Remove Largo's pseudoelement ::before and ::after lines
• Replace them with borders
  • check padding/spacing/margins to nearby content
• Test this change against:
  • pull quote blocks
  • blockquote blocks with an added .type-pull-quote class
  • Module Wrapper content
  • other testing concerns in Block quote styles #1687

[benlk]

Example styles for this can be seen in INN/umbrella-workdayminn#9