v5: Update badges

First pass at updating the badge component per discussions in #27136, other threads, and our team Slack channel. Here's what's included thus far:

• Drop hover and focus states
• Drop .badge-* variants and associated mixin for .bg-* utilities
• Drop .badge-pill for .rounded-pill utility and adjust horizontal padding to find middle ground of .badge and old .badge-pill
• Remove unused variables
• Add default color value to .badge base class
• Update docs to reflect changes