Panorama: Update for vertical navigation; implement custom width

[marcustyphoon]

Description

This reimplements Panorama after the vertical navigation UI changes, adds a preference for the maximum post column width, and fixes a number of elements that were not correctly widened in Panorama's previous iteration (some of which I never bug reported, like link elements).

(The default width, pre-reblog-redesign, corresponds to the 3-column masonry view on the explore page. Post reblog redesign it's totally arbitrary at the moment.)

It is somewhat awkward due to Redpop's use of the same wrapper elements around the main page content and right sidebar regardless of the contents of said main page content. Without the use of :has, it is very difficult to do behavior conditional on e.g. the settings page rather than the post column being the main page contents when using a pure CSS solution. I thought a little bit about whether pageModifications would be helpful here, but it's not immediately obvious to me what one would target and what one would toggle. I bet that's eventually the best path forward though.

At the moment, this can't handle the reblog redesign, so it should stay a draft until that experiment ends in either direction.

Resolves #814, resolves #985, resolves #1026, resolves #1109, resolves #1041, resolves discussion #391, resolves discussion #853, resolves discussion #1145.

Resolves #860.

Resolves half of #937, the tag page portion; blog view panorama is more complicated.

Testing steps

[marcustyphoon]

(Note that this only works when the screen is very wide; I'm sure certain people would like the post column to be widened in cases where that would necessitate collapsing the left and right rails, but a) no idea what Tumblr plans to do in that regard if anything and b) because of how media queries work I'm not sure it's really realistic to even attempt.)

[marcustyphoon]

Note: This should be significantly easier, and can be somewhat more feature rich, by taking advantage of :has().

Edit: Eh... kind of. It makes handling the "I navigated from the dashboard to a page that should not be expanded" case easier to guarantee, but it's arguably cleaner to keep using a mutation observer to mark active timelines to simplify the post CSS, at which point how much value are you getting out of it? And this is... sort of readable, but it's not the greatest.

${mainContentWrapper}:has(> div > div > ${mainPostColumn}) {

}
${mainContentWrapper} > div:has(> div > ${mainPostColumn}) {

}
${mainContentWrapper} > div > div:has(> ${mainPostColumn}) {

}
${mainContentWrapper} > div > div > ${mainPostColumn} {

}

[marcustyphoon]

Now featuring: Tumblr Patio support! Optional preference not to expand media in posts that centers the media instead! Bug fixes for ad containers (yes, really)!