chore: update xkit-controls-row styles

[marcustyphoon]

Description

In #1904, we made some changes to the xkit-controls-row element that our control button creates so that we can insert control buttons into editable posts without edit/delete buttons, i.e. those with the new footer. Tumblr then added back the edit/delete buttons in a new postOwnerControls element just when we thought we were done, making the xkit-controls-row element currently completely unused. We left it in as a fallback but didn't touch it further.

This updates it to match the current postOwnerControls element, both with and without Classic Footer enabled, so that if it does ever get used as a fallback (or if we want to add control buttons to a non-editable post), its appearance will be consistent.

Its position in the DOM, spacing, and bottom border line should be correct. Notably, this includes making the line span from post edge to post edge in non-classic-footer mode, which I personally think looks bad. But that's how Tumblr's element looks!

Tumblr's element was just changed today, illustrating that it's more likely to be changed again during this general timeframe, so in a sense this doesn't make much sense to merge now. Also, you know... at all, one could make the argument.

Testing steps

• Un-revert the test commits and enable Quick Tags and Trim Reblogs so that control buttons appear using the xkit-controls-row on non-editable posts.
• Open your dash and your channel page side by side and confirm that the position in the DOM, spacing, and bottom border lines on the footer rows with the Quick Tags/Trim Reblogs buttons match.
• Enable Classic footer and confirm that the position in the DOM, spacing, and bottom border lines on the footer rows with the Quick Tags/Trim Reblogs buttons match.