* Ensure correct active class is set on button toggles/checkboxes/radios on page load
Sanity check, ensures that the UI visually matches the actual values/states of controls. Also ensures that if any autocomplete/autofill happened, this is visually accounted for
by having the correct class set.
Includes unit tests (and `autocomplete` has been removed from these as it's no longer necessary)
* Remove now unnecessary autocomplete attribute
As the attribute was there to force/ensure that the visual presentation matched the state, and this is now taken care of programmatically, there's no need to unnecessarily suppress autocomplete...let them autocomplete if they want to...
- adds more defensive checks to make sure no unnecessary toggling happens on disabled buttons; this also fixes an up-to-now undiscovered bug where a toggle button with `.disabled` class would still have its `aria-pressed` toggled
- adds a set of explicit tests for the above case of disabled buttons and `aria-pressed`
- remove a now irrelevant (or at least very nonsensical) test for `<label>` containing both an actionable and a `hidden` `<input>`
- expand the test for disabled checkbox to also explicitly test starting conditions (used mainly in my debugging)
- ensure that `$btn[0].click()` is used to click checkboxes in tests, rather than the `click()` on the jquery object which is simply a shorthand for `trigger('click')` and does not actually trigger the browser default behavior
- remove the `preventDefault()` from the button handling, which was preventing correct keyboard functionality for checkboxes/radio buttons
- add extra logic to the button.js code to handle checkboxes correctly and avoid double-triggering as a result of mouse interactions (which saw the checkboxes being toggled twice, thus returning them to their original state)
- add logic that prevents the `checked` property from being added incorrectly for any inputs other than radio buttons and checkboxes
- added more tests (including the most basic test for a properly triggered fake checkbox button)
- work around Firefox bug #1540995 (which this code was hitting after removing the `preventDefault()`, due to Firefox's incorrect toggling of disabled checkboxes when programmatically (but not manually) activated with a `click()` event
- Add same advice about keyboard/AT handling to popovers as a callout; also add information about not adding excessive content or interactive controls (and the suggestion to opt for a modal)
- Tweak the tooltips callout for consistency
Extrapolates the previously used selector into a new mixin that only generates valid CSS by creating psuedo-classes for `valid` and `invalid`, and nothing else.
Fixes#28380.
