[META] Make Olivero the default theme

Adding #3230435: Makes sure Olivero JS is a small as possible here because it's only necessary when we flip the switch on the default theme, not to make the theme stable.

Adding some tags.

Moving #3173877: [meta] QA testing of Olivero across multiple browsers to this issue, I don't think the last couple of browsers should hold up marking Olivero stable in 9.3, but it'd be good to be sure we've gone through everything prior to making it the default?

Agreed! Fixing the notation so it is properly included.

Adjusting title, since 9.3 released

Still time to get this into 9.4.0, so moving back to there.

There are a number of accessibility issues on #3177296: [META] Make Olivero stable that were described as:

Should-have issues for stable release / settings as default theme:

Should they be added to the IS here? Thanks!

Added the should-haves from the previous meta.

(Removing issues that have been closed in the interim.)

The fact that it came up in an a11y review is still a reason to keep it as a should-have (even if it's not a must-have). :)

New one, seems at least should-have: #3270574: Olivero comment template breaks 'new' indicator/anchor

#3173877: [meta] QA testing of Olivero across multiple browsers was just marked complete based on the remaining Safari work done, so #3219959: Update standard profile so Olivero is the default theme is the only must have left.

As a Drupal core product manager, I approve of Olivero becoming the default. The amount of improvements this has over Bartik is immense. I don't believe there are any missing pieces or problems from a product perspective for a default theme that will be a big step up from Bartik.

Went through the queue and discussed with @ckrina at DrupalCon Portland 2022 and we agreed that after the roadmap in the issue summary has been resolved, Olivero can be marked as the default theme in Standard.

All of the blockers (except the actual issue to make Olivero the default) are done, and most of the should haves are either done or need review, so happy to remove release manager review tag here. A lot of other bugfixes and features have landed since the theme marked was marked stable that didn't get explicitly listed in this issue too, which is a good sign in general.

I've also been using a subtheme (shh) of Olivero for a personal project, and have been really impressed (also found and posted a couple of bugs).