New custom form helpers

[cpsievert]

Essentially wrappers around https://getbootstrap.com/docs/5.0/forms/overview/ (we'll probably want to require BS5 and above since the CSS/Sass has changed drastically)

• input_switch()
• input_slider()
• input_select()
• input_radio()
• input_check()
• input_check_group()

Floating labels should be easy to implement -- also make sure these work well with shinyvalidate

[cpsievert]

Some of these may also need an inline arg to make them work better when inlined inside of something like a card header