Add new interaction utilities and role attr to Reboot (#30562)

- Adds .user-select-* utils from v5
- Adds button role attribute util, one of the top requested features in our issues for adding pointer cursors
- Adds new docs page to demonstrate both
- Includes Sass list for customizing user select

scss/_variables.scss

@@ -1138,6 +1138,7 @@ $pre-scrollable-max-height:         340px !default;
 $displays: none, inline, inline-block, block, table, table-row, table-cell, flex, inline-flex !default;
 $overflows: auto, hidden !default;
 $positions: static, relative, absolute, fixed, sticky !default;
+$user-selects: all, auto, none !default;
 
 
 // Printing