Decouple Stable libraries from Bartik/Seven/Claro/Umami

Decouples libraries and adds tests based on ThemeNotUsingClassyLibraryTest.

Both libraries are for BC support but have not yet been deprecated so unsure which branches this would be applied to.

Instead of overriding the JavaScript theme functions, it would be nice if we could fix regressions caused by falling back to the default module markup.

I'm pleased to hear this is an option! Perhaps backwards-compatibility-fatigue got in the way of me seeing it as a feasible one.

I'm of the opinion that stable/drupal.ajax is not necessary in any of the core themes.

I compared the markup in each core theme with and without stable/drupal.ajax. Note that the markup is the same in each theme so no theme-specific examples are needed.

Ajax progress bar markup WITH stable/drupal.ajax

<div aria-live="polite" class="progress ajax-progress ajax-progress-bar" id="ajax-progress-edit-field-bar-0-upload-button">
	<div class="progress__label">
		&nbsp;
	</div>
	<div class="progress__track">
		<div class="progress__bar"></div>
	</div>
	<div class="progress__percentage"></div>
	<div class="progress__description">
		&nbsp;
	</div>
</div>

Ajax progress bar markup WITHOUT stable/drupal.ajax

<div class="ajax-progress ajax-progress-bar">
	<div aria-live="polite" class="progress" id="ajax-progress-edit-field-bar-0-upload-button">
		<div class="progress__label">
			&nbsp;
		</div>
		<div class="progress__track">
			<div class="progress__bar"></div>
		</div>
		<div class="progress__percentage"></div>
		<div class="progress__description">
			&nbsp;
		</div>
	</div>
</div>

This confirms the only difference is from #3059847: Move hard coded AJAX progress bar classes to a theme function
The backwards compatibility provided by stable/drupal.ajax is not required by any of the core themes. Manual testing confirmed that moving the classes ajax-progress ajax-progress-bar to a wrapper div has no visual or functional difference.

Tagging with needs issue summary update - which will be addressed once I've determined if stable/drupal.user is necessary.

No interdiff as this is a fully different approach from earlier patches.

After determining stable/drupal.ajax does not need to be addressed in core themes, that leaves stable/drupal.user, which needs to be addressed in Bartik, Seven and Umami. This was a BC layer added in #3061265: Use specific class for password confirm message, where the password confirm message class was changed.. Without the stable library, the core themes should use the new class. The specific functionality to look for is that the text following "Passwords match:" in password confirm messages should be green/red depending on the match status.

For now, the css rules have been expanded to cover both selectors, with a @toto to remove the old one once Stable is no longer a base theme in #3115223: Remove Stable as a base theme of core themes

Here's how it looks with the manual testing patch:

The suggestion in #10 is a good one. Without that, it's incredibly unlikely that any regressions would be caught, and it makes things difficult to test. It is a good use of beta release status. Applying this change required more steps than anticipated, but I still think it's a good idea.

The patch in #11 did not include a few files. Interdiffing from 8 as that is the accurate change

Needed to reroll after #3115088: Remove Classy as a base theme of core themes
After the reroll, quite a bit of this patch is for the temporary inclusion of theme function as suggested in #10. I still think this is a good idea -- but if those specific changes are slowing this down it may be worth skipping as there's only one issue other than this one that needs to land before core themes don't need to declare Stable as a base theme: #3113211: Create test for theme asset decoupling from Stable and address any regressions that decoupling may cause

Once that issue and this one is done, #3115223: Remove Stable as a base theme of core themes can be reviewed (in that issue, there's already a patch to get all the tests passing, so things can potentially move quickly).