.btn-body and .btn-outline-body

[ngblaylock]

This would take off a lot of bloat that .btn-base-* would.

Make this opt in as well.

[ngblaylock]

https://github.com/twbs/bootstrap/issues/37753

This mentions using .btn-body and .btn-outline-body, and suggests doing .btn-monochrome and .btn-outline-monochrome.

[ngblaylock]

• .btn-body
• .btn-theme
• .btn-contrast
• .btn-reactive
• .btn-neutral
• .btn-adaptive