Creating max-width images is not dependent on the display, so setting it is redundant. Cleans up the comments and implementation of the mixin as well.
Fixes#20767
- Move and rename .img-rounded to .rounded, .img-circle to .rounded-circle
- Add new .rounded-{direction} utils
- New docs pages for border utils with TBD comments for the border property
- Removes most image examples for rounding from the content/images docs in favor of new docs page
- 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)
