Standardize focus styles using focus-ring mixin (#41950)

Standardize focus styles using focus-ring mixin (#41950)

* Standardize focus styles using focus-ring mixin

Replace box-shadow focus styles with consistent focus-ring() mixin across components:
- Accordion, nav, pagination now use @include focus-ring(true)
- Forms (checkboxes, radios, switches, range, controls) use focus-ring mixin
- Update focus-ring-offset default from -1px to 1px
- Remove deprecated *-focus-box-shadow variables

* Fix some focus styles

* Remove unused CSS

* Remove more box-shadow on buttons