Since the "remote" option is no longer available in v4 the reference to the "loaded.bs.modal" event is no longer needed, too.

v4: Couple popover fixes

Make named anchor/placeholder link style reset more specific

v4: Card improvements

Here we're doing some margin swapping, so it looks a little funky. All this does is match the margin implementation and rendering across our table and flex versions of card decks.

- Remove background-color from header and footer in inverse cards (fixes #19841)
- Update border override for header and footer in cards; only need to declare a new color
- Update the selector for targetting blockquote footers in cards

- Remove the box-shadow and switch back to border to match .card basics
- Update the header nav margin override--since we restored the border, we need that default negative margin at the bottom

- Add inverse examples for all variants
- Use rgba() colors for hover and accent states for easy usage in inverse styles

Update tags/labels/badges migration docs to mention class and change in behavior for alignment in list groups

v4: Figuring out split dropdown buttons

- Really we didn't need to do any of that strip units stuff to generate six new variables, two for each button size
- Using sibling selectors, we can target those split button dropdown toggles using the .dropdown-toggle-split class, and adjust padding and margin as needed
- Now, we nuke the margin-left from the ::after generated caret and tighten up the padding so that those split toggles don't look huge next to their main button

v4: Forms cleanup

Handle aria-hidden on modal container when showing/hiding

Fixes #19878

- Includes new class
- New docs to support it
- Rearranged older docs

This avoids applying the reset to named anchors/placeholder links (links
without an `href`) that have explicitly been made keyboard-focusable
(using `tabindex`). This is not fool-proof - it's not
easy/straightforward to check for the actual `tabindex` value itself, to
ensure it's positive, not will this apply if a link has been "blessed"
with `tabindex` via JS. However, this should catch most common uses (and
gives a reasonably valid way around the issue for developers who, for
whatever reason, DO want to use links without `href` - as side effect,
it forces best practice of at least ensuring these links can also be
focused with the keyboard)