- Move disabled radio and checkbox styles to Reboot
- Collapse .radio and .checkbox into single class, .form-check
- Collapse .radio-inline and .checkbox-inline into single class, .form-check-inline
- Require classes for sub-elements in both new classes

- Rather than use CSS hacks, let's avoid needing to hack anything
- Creates a new Reboot entry to simply reset the appear of the temporal inputs, thereby avoiding the problem entirely
- Less than ideal for conveying affordance on iOS, but given bugginess of the input itself, seems a decent tradeoff

Fixes #18573: Change name of .form-control-label to .col-form-label (and .form-control-legend to .col-form-legend) to reiterate use for only grid layouts

Uses a new more specific class, adds some basic spacing, and clarifies
that this class is only for validation feedback.

Clears up the help text class question in
https://github.com/twbs/bootstrap/pull/18704#issuecomment-168241731 and
addresses the vertical spacing in #18703.

Move to a translucent input border with background-clip: padding-box for improved blending across different background-colors

[skip sauce]
[skip validator]

[skip sauce]
[skip validator]

- Moves from no set line-height (inherited of 1.5) to declared 1.25 for
all inputs and buttons (regardless of size modifier).

- Updates padding to be `.5rem` instead of `.375rem` so that padding is
more likely to be whole numbers based on the root font-size.

- Whole numbers will be beneficial in avoiding odd fractional pixels
that can lead to misalignment as shown in #18607.

- Large buttons and inputs are now a tad wider, and smaller
buttons/inputs a tad shorter and narrower, too.

[skip sauce]
[skip validator]

- Rename -height to -height-base to match other vars
- Drop use of -height across the board and rely on it to be inherited
- Adjust padding of .dropdown-header to account for different line-height of h6 heading element (this needs refactoring for variables and rems also)

[skip sauce]

Switch to actually-Safari-specific CSS hack when fixing vertical alignment of temporal input text in iOS Safari

See http://browserbu.gs/css-hacks/webkit-full-page-media/
Fixes #17308

[skip sauce]
[skip validator]

Erratum of #18778

[skip sauce]
[skip validator]

Both widgets need to use the same border width because of input groups.
Thus:
$btn-border-width   => $input-btn-border-width
$input-border-width => $input-btn-border-width

[skip sauce]

[skip sauce]

Refs b6e6a05b
We ought to re-check this for iOS 9.1 at some point...

[skip sauce]
[skip validator]

Reunites the family.
Closes #17791

fixes border-width issues when customizing font-size by using 1px instead of .0625rem as default -width