[Docs] Clarify suggested use of custom validation styles, add note about resetting form appearance after validation (#25628)

* Expand/clarify recommendation for using custom validation styles

Seems support for correctly announcing browser default navigation bubbles/notifications has improved recently. Now it seems only Chrome (at least on Win and Android, not tested on macOS) is the odd one out.

However, we should really make sure the custom validation messages are also tied correctly to their relevant form controls - need to dig out the PR that will ensure that.

* Add note about resetting form appearance after submission

xref https://github.com/twbs/bootstrap/issues/25626

Closes https://github.com/twbs/bootstrap/issues/25611

2 small typos

Fixes #25235

* Dropdown - Allow to disable Popper.js style

* Update dropdown.js

* Update dropdown.html

* copy changes

* add missing properties

list of new properties:
align-content
animation-fill-mode
appearance
column-count
column-fill
column-gap
column-rule
column-rule-color
column-rule-style
column-rule-width
column-span
column-width
columns
direction
fill
flex-shrink
orphans
page-break-after
page-break-before
page-break-inside
perspective
src
stroke
unicode-bidi
widows

* fix invalid JSON config

add curly brackets

* Update .stylelintrc

* Remove clip-path from .sr-only utility as it causes perf regressions in Chrome

* change snippet to example

* set color to `.form-control-plaintext`
* fixes readability on dark themes like ‘darkly’
  * https://bootswatch.com/darkly/index.html#forms
  * https://bootswatch.com/slate/index.html#forms
  * https://bootswatch.com/superhero/index.html#superhero
  * https://bootswatch.com/solar/index.html#forms

/cc @thomaspark

* Add note about insert position of "map-remove"

* Use optional keys instead of required keys

* use $input-bg for $custom-select-bg

This checks if all variables are `!default`.

Clarify migration docs to remove mention of .table-responsive being for the parent element vs the table element itself (#25539)

Fixes #25413

* Prevent focus into closed offcanvas

- Fixes typo with "with at" in "horizontal with at the small breakpoint"

* Move helpful code comments

* Add .carousel-fade option to Sass

* Document example of the fade carousel

* more logical warning of the .active class on carousel items

* Add .dropdown-item-text class

* Add example of plain text within a .dropdown-menu, too

* reorganize, simple/clearer headings

Currently bootstrap only provides 4 variations of `width` and `height` css utilities, which are:

1. 25%
2. 50%
3. 75%
4. 100%.

Here, I'm adding `auto` to the list. This is useful when we need to reset the width/height value
back to the browser default value at some point.

Closes #25313

Less on 2 symbols