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/layouts/_default/docs.html

@@ -1,29 +1,45 @@
 {{ define "main" }}
-  {{ partial "docs-subnav" . }}
-
-  <div class="container-xxl my-md-4 bd-layout">
+  <div class="container-xxl bd-gutter mt-3 my-md-4 bd-layout">
     <aside class="bd-sidebar">
-      {{ partial "docs-sidebar" . }}
+      <div class="offcanvas-lg offcanvas-start" id="bdSidebar" aria-labelledby="bdSidebarOffcanvasLabel">
+        <div class="offcanvas-header border-bottom">
+          <h5 class="offcanvas-title" id="bdSidebarOffcanvasLabel">Browse docs</h5>
+          <button type="button" class="btn-close" data-bs-dismiss="offcanvas" aria-label="Close" data-bs-target="#bdSidebar"></button>
+        </div>
+
+        <div class="offcanvas-body">
+          {{ partial "docs-sidebar" . }}
+        </div>
+      </div>
     </aside>
 
     <main class="bd-main order-1">
-      <div class="bd-intro ps-lg-4">
+      <div class="bd-intro pt-2 ps-lg-2">
         <div class="d-md-flex flex-md-row-reverse align-items-center justify-content-between">
-          <a class="btn btn-sm btn-bd-light mb-2 mb-md-0" href="{{ .Site.Params.repo }}/blob/main/site/content/{{ .Page.File.Path | replaceRE `\\` "/" }}" title="View and edit this file on GitHub" target="_blank" rel="noopener">View on GitHub</a>
-          <h1 class="bd-title" id="content">{{ .Title | markdownify }}</h1>
+          <a class="btn btn-sm btn-bd-light mb-3 mb-md-0 rounded-2" href="{{ .Site.Params.repo }}/blob/main/site/content/{{ .Page.File.Path | replaceRE `\\` "/" }}" title="View and edit this file on GitHub" target="_blank" rel="noopener">
+            View on GitHub
+          </a>
+          <h1 class="bd-title mb-0" id="content">{{ .Title | markdownify }}</h1>
         </div>
         <p class="bd-lead">{{ .Page.Params.Description | markdownify }}</p>
         {{ partial "ads" . }}
       </div>
 
       {{ if (eq .Page.Params.toc true) }}
-        <div class="bd-toc mt-4 mb-5 my-md-0 ps-xl-3 mb-lg-5 text-muted">
-          <strong class="d-block h6 my-2 pb-2 border-bottom">On this page</strong>
-          {{ .TableOfContents }}
+        <div class="bd-toc mt-3 mb-5 my-lg-0 ps-xl-3 mb-lg-5 text-muted">
+          <button class="btn btn-link link-dark p-md-0 mb-2 mb-md-0 text-decoration-none bd-toc-toggle d-md-none" type="button" data-bs-toggle="collapse" data-bs-target="#tocContents" aria-expanded="false" aria-controls="tocContents">
+            On this page
+            <svg class="bi d-md-none ms-2" aria-hidden="true"><use xlink:href="#chevron-expand"></use></svg>
+          </button>
+          <strong class="d-none d-md-block h6 my-2">On this page</strong>
+          <hr class="d-none d-md-block my-2">
+          <div class="collapse bd-toc-collapse" id="tocContents">
+            {{ .TableOfContents }}
+          </div>
         </div>
       {{ end }}
 
-      <div class="bd-content ps-lg-4">
+      <div class="bd-content ps-lg-2">
         {{ if .Page.Params.sections }}
           <div class="row g-3">
             {{ range .Page.Params.sections }}