Floating labels new filled and improved outlined support

Here is a first patch, and this is still work in progress.

This patch fully works and covers all functionality and changes described in issue description. Additionally some refactoring of current floating label CSS code is done.

Some of changes from #3256665-6: Browsers are changing input bg color on autofill went into this patch, here is a clean version.

One refactoring change was a bit too much.

Outline autofill fix should use body-bg so it looks transparent.

input-group selector somehow went missing.

Some basic floating rules should not be applied to radio and checkbox input elements.

Floating label disabling can now be done also with a CSS class `form--floating-labels-off` (use it in webforms builder). Information about disabling per form is now passed to form children so they are correctly render.

Hmmm, changes in the latest patch are now dependent on changes in #3256688: Floating labels input has left or right border radius reset so this patch now depends on patch in that issue.

Documentation related to this new changes is updated on https://www.drupal.org/docs/8/themes/bs-base/additional-features/floatin....

Testings are showing two things:

- For select we should assume always that label position is in active state because select most of the time have a label for none/empty value. Assuming other way leads to a bug when you select none option, in this case currently, label will overlap with select empty value label.
- Position of label in textarea is too low. Idea here was that on focus input caret stays on the same place where label was, but this looks ugly. We should reposition textarea label to be on the same place as in textfield.

New patch is fixing this two things.

New version of the patch, changes:

- Use form-group--floating-label for CSS selectors so we can disable floating label per element when needed.
- Support more elements: color, datetime, entity_autocomplete, machine_name, webform_autocomplete, webform_time.

There is a problem with a webform address element - address ajax loaded elements are not floating label enabled. The problem is that bs_bootstrap_preprocess_form_element() is not called on ajax form update. Will try to figure that out.

Small fix for floating label outline wrong padding on empty selection.

Forgot to fully remove focus and filled selectors in previous patch.

Some additional fixes for composite forms and active label bg color.

More fixes and improvements:

• Removed most of form-composite last child CSS rules - it is complex to do this properly, exact design definition is missing and webforms are doing all kind of weird stuff with html and ajax reload elements (like advanced address). By removing rules layout behaviour is more predictable and actually looks better across various combinations. Maybe later we can improve this.
• Some fixes for filled floating labels for elements without a label - style was missing. Also focusing element height change is fixed for textarea and elements without a label.
• Enabling floating label on elements in code is additionally improved and now also works for form ajax reload parts. Thanks @Berdir for helping debug form ajax reload problem.

> this works for webform I guess

Yeah you are right, added checking for address, datetime and password_confirm types.

Note that datetime is currently not working fully because html is quite different and floating label rules are not working fully for this case. I guess we will fix that in follow-up if needed.

Floating label outline for select box CSS is not setting select box bg transparent when label is missing.

Committed.