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/code-examples.js

@@ -0,0 +1,88 @@
+// NOTICE!! DO NOT USE ANY OF THIS JAVASCRIPT
+// IT'S ALL JUST JUNK FOR OUR DOCS!
+// ++++++++++++++++++++++++++++++++++++++++++
+
+/*!
+ * JavaScript for Bootstrap's docs (https://getbootstrap.com/)
+ * Copyright 2011-2022 The Bootstrap Authors
+ * Copyright 2011-2022 Twitter, Inc.
+ * Licensed under the Creative Commons Attribution 3.0 Unported License.
+ * For details, see https://creativecommons.org/licenses/by/3.0/.
+ */
+
+/* global ClipboardJS: false, bootstrap: false */
+
+(() => {
+  'use strict'
+  // Insert copy to clipboard button before .highlight
+  const btnTitle = 'Copy to clipboard'
+  const btnEdit = 'Edit on StackBlitz'
+
+  const btnHtml = [
+    '<div class="bd-code-snippet">',
+    '   <div class="bd-clipboard">',
+    '      <button type="button" class="btn-clipboard">',
+    '        <svg class="bi" width="1em" height="1em" fill="currentColor" role="img" aria-label="Copy"><use xlink:href="#clipboard"/></svg>',
+    '      </button>',
+    '   </div>',
+    '</div>'
+  ].join('')
+
+  // wrap programmatically code blocks and add copy btn.
+  document.querySelectorAll('.highlight')
+    .forEach(element => {
+      if (!element.closest('.bd-example-snippet')) { // Ignore examples made be shortcode
+        element.insertAdjacentHTML('beforebegin', btnHtml)
+        element.previousElementSibling.append(element)
+      }
+    })
+
+  /**
+   *
+   * @param {string} selector
+   * @param {string} title
+   */
+  function snippetButtonTooltip(selector, title) {
+    document.querySelectorAll(selector).forEach(btn => {
+      bootstrap.Tooltip.getOrCreateInstance(btn, { title })
+    })
+  }
+
+  snippetButtonTooltip('.btn-clipboard', btnTitle)
+  snippetButtonTooltip('.btn-edit', btnEdit)
+
+  const clipboard = new ClipboardJS('.btn-clipboard', {
+    target: trigger => trigger.closest('.bd-code-snippet').querySelector('.highlight')
+  })
+
+  clipboard.on('success', event => {
+    const iconFirstChild = event.trigger.querySelector('.bi').firstChild
+    const tooltipBtn = bootstrap.Tooltip.getInstance(event.trigger)
+    const namespace = 'http://www.w3.org/1999/xlink'
+    const originalXhref = iconFirstChild.getAttributeNS(namespace, 'href')
+    const originalTitle = event.trigger.title
+
+    tooltipBtn.setContent({ '.tooltip-inner': 'Copied!' })
+    event.trigger.addEventListener('hidden.bs.tooltip', () => {
+      tooltipBtn.setContent({ '.tooltip-inner': btnTitle })
+    }, { once: true })
+    event.clearSelection()
+    iconFirstChild.setAttributeNS(namespace, 'href', originalXhref.replace('clipboard', 'check2'))
+
+    setTimeout(() => {
+      iconFirstChild.setAttributeNS(namespace, 'href', originalXhref)
+      event.trigger.title = originalTitle
+    }, 2000)
+  })
+
+  clipboard.on('error', event => {
+    const modifierKey = /mac/i.test(navigator.userAgent) ? '\u2318' : 'Ctrl-'
+    const fallbackMsg = `Press ${modifierKey}C to copy`
+    const tooltipBtn = bootstrap.Tooltip.getInstance(event.trigger)
+
+    tooltipBtn.setContent({ '.tooltip-inner': fallbackMsg })
+    event.trigger.addEventListener('hidden.bs.tooltip', () => {
+      tooltipBtn.setContent({ '.tooltip-inner': btnTitle })
+    }, { once: true })
+  })
+})()