Add horizontal list group modifier (#27970)

Alternate take to #27683 that builds the modifier class based on min-width, such that list groups are stacked until the class's breakpoint is reached. This is less verbose, matches our primary responsive approach, and prevents an extra class. Unfortunately, I believe supporting flush list groups is too much code here, so I've skipped that and made a note in the docs.

Also added examples generate from our breakpoints data file with a protip for how to do equal width items.

site/docs/4.2/assets/scss/_component-examples.scss

@@ -246,6 +246,9 @@
 .bd-example > .list-group {
   max-width: 400px;
 }
+.bd-example > [class*="list-group-horizontal"] {
+  max-width: 100%;
+}
 
 // Navbars
 .bd-example {