v5.2.0 design refresh, plus responsive offcanvas classes (#35736)

* Add responsive offcanvas classes

- Updates navbar-expand classes to de-dupe some styles—these shouldn't interfere now.
- Adds some JS to the offcanvas component to help with responsiveness

Co-Authored-By: GeoSot <geo.sotis@gmail.com>

* Redesign homepage, docs, and examples

Homepage:

- New Bootstrap purple navbar
- Redesigned masthead
- Rewrote and redesigned homepage content
- Replace Copy text with icons like Bootstrap Icons site across all ClipboardJS instances
- Fixed padding issues in site footer
- Match homepage button styles to examples page, use gap instead of tons of responsive margin utils

Docs:

- New navbar, no more subnav. Migrated search and version picker into the main navbar and refreshed the design of it all, including the responsive toggles.
- New sidebar navigation is always expanded, and now features Bootstrap Icons alongside section headings
- Sidebar navigation autoscrolls to active link for better usability
- Subnav and navbar padding issues ironed out
- Enhanced the version picker in anticipation of v5.2: we can now link right to the same page in the previous version.
- Redesign callouts to add more color to our pages
- Collapse table of contents on mobile
- Cleanup and redesign button styles with CSS variables
- Update design for subnav version dropdown
- Update highlight and example to be full-width until md
- Improve the Added In badges
- Turn the ToC into a well on mobile
- Redesign code snippets to better house two action buttons

Examples:

- Redesign Examples page layout
- Add new example for responsive offcanvases in navbars

* Convert offcanvas to CSS vars

* Feat: add resize handler to Offcanvas.js.

If we could use as default the `.offcanvas` class without modifiers, we then, could add a simplified selector
The selector itself, ignores the .offcanvas class as it doesn't have any responsive behavior
The `aria-modal` addon is to protect us, selection backdrop elements

* Separate examples code, Add some selectors, fix stackblitz btn

Co-authored-by: GeoSot <geo.sotis@gmail.com>

site/assets/js/search.js

@@ -14,12 +14,17 @@
   const siteDocsVersion = inputElement.getAttribute('data-bd-docs-version')
 
   document.addEventListener('keydown', event => {
-    if (event.ctrlKey && event.key === '/') {
+    if ((((event.ctrlKey || event.metaKey) && event.key === 'k')) || (event.ctrlKey && event.key === '/')) {
       event.preventDefault()
       inputElement.focus()
     }
   })
 
+  if (navigator.platform.includes('Win') || navigator.platform.includes('Linux')) {
+    const searchShortcut = document.querySelector('.bd-search')
+    searchShortcut.setAttribute('data-shortcut', '⌃K')
+  }
+
   window.docsearch({
     apiKey: '5990ad008512000bba2cf951ccf0332f',
     indexName: 'bootstrap',