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>

js/tests/unit/offcanvas.spec.js

@@ -155,6 +155,28 @@ describe('Offcanvas', () => {
         offCanvas.show()
       })
     })
+
+    it('should call `hide` on resize, if element\'s position is not fixed any more', () => {
+      return new Promise(resolve => {
+        fixtureEl.innerHTML = '<div class="offcanvas-lg"></div>'
+
+        const offCanvasEl = fixtureEl.querySelector('div')
+        const offCanvas = new Offcanvas(offCanvasEl)
+
+        spyOn(offCanvas, 'hide').and.callThrough()
+
+        offCanvasEl.addEventListener('shown.bs.offcanvas', () => {
+          const resizeEvent = createEvent('resize')
+          offCanvasEl.style.removeProperty('position')
+
+          window.dispatchEvent(resizeEvent)
+          expect(offCanvas.hide).toHaveBeenCalled()
+          resolve()
+        })
+
+        offCanvas.show()
+      })
+    })
   })
 
   describe('config', () => {