One-Click Postage: Restore functionality on accounts with new footer variant

[marcustyphoon]

Description

This restores basic One-Click Postage functionality on accounts with one of Tumblr's new post footer tests.

XKit Rewritten's Quick Reblog has already had a number of fixes for this footer variant (as well as another one). For reference, I squashed them here: AprilSylph/XKit-Rewritten@728fd65. Most of these fixes are for things that don't even work in this project currently, though.

AlreadyReblogged in particular does not currently work (as noted in #2098), so I did not fix it here. It is, it should be noted, fairly annoying to fix.

For consistency with this repository's norms, particular consideration must be made to browser compatibility; New XKit supports older browser versions that do not support :has() selectors.

Testing steps

Conform that, on an account without the new post footer:

• The One-Click Postage menu appears when hovering the mouse over a post's reblog button
• The One-Click Postage menu disappears when moving the mouse off of a post's reblog button
• The One-Click Postage menu does not disappear when moving the mouse off of a post's reblog button if a text box within the menu is active
• The One-Click Postage menu does not appear when hovering the mouse over a post's reblog button if the post has reblogs disabled
• The One-Click Postage menu works

Conform that, on an account with the latest new post footer:

• The One-Click Postage menu appears when hovering the mouse over a post's reblog button
• The One-Click Postage menu disappears when moving the mouse off of a post's reblog button
• The One-Click Postage menu does not disappear when moving the mouse off of a post's reblog button if a text box within the menu is active
• The One-Click Postage menu does not appear when hovering the mouse over a post's reblog button if the post has reblogs disabled (and has at least one reblog; will appear normal)
• The One-Click Postage menu does not appear when hovering the mouse over a post's reblog button if the post has reblogs disabled (and has zero reblogs; the button will appear greyed out)
• The One-Click Postage menu disappears after clicking a post's reblog button to open the Tumblr reblog menu
• The One-Click Postage menu does not appear when hovering the mouse over a post's reblog button when the Tumblr reblog menu is open
• The One-Click Postage menu works

XKit team members, message me if you want to test this and don't have accounts both with and without the relevant flag.

[marcustyphoon]

• Test this in Firefox 115
• Smoke test this in up-to-date Firefox
• Smoke test this in Chrome 102
• Smoke test this in up-to-date Chrome

[hobinjk]

LGTM, I've low-rolled my A-B testing and haven't experienced the new UI so hopefully this works over there!

[marcustyphoon]

This is the kind of PR I'm kind of terrified of pressing merge on without April. But, eh. Should be fine.