Move inline SVGs to includes. (#23297)

Also:

* compress them with SVGOMG
* add titles
* add `focusable="false"`

_includes/icons/bootstrap.svg

-<svg {% if include.class %} class="{{ include.class }}"{% endif %}{% if include.width %} width="{{ include.width }}"{% endif %}{% if include.height %} height="{{ include.height }}"{% endif %} viewbox="0 0 612 612" xmlns="http://www.w3.org/2000/svg" focusable="false"><title>Bootstrap</title><path fill="currentColor" d="M510 8a94.3 94.3 0 0 1 94 94v408a94.3 94.3 0 0 1-94 94H102a94.3 94.3 0 0 1-94-94V102a94.3 94.3 0 0 1 94-94h408m0-8H102C45.9 0 0 45.9 0 102v408c0 56.1 45.9 102 102 102h408c56.1 0 102-45.9 102-102V102C612 45.9 566.1 0 510 0z"/><path fill="currentColor" d="M196.77 471.5V154.43h124.15c54.27 0 91 31.64 91 79.1 0 33-24.17 63.72-54.71 69.21v1.76c43.07 5.49 70.75 35.82 70.75 78 0 55.81-40 89-107.45 89zm39.55-180.4h63.28c46.8 0 72.29-18.68 72.29-53 0-31.42-21.53-48.78-60-48.78h-75.57zm78.22 145.46c47.68 0 72.73-19.34 72.73-56s-25.93-55.37-76.46-55.37h-74.49v111.4z"/></svg>
+<svg{% if include.class %} class="{{ include.class }}"{% endif %}{% if include.width %} width="{{ include.width }}"{% endif %}{% if include.height %} height="{{ include.height }}"{% endif %} viewbox="0 0 612 612" xmlns="http://www.w3.org/2000/svg" focusable="false"><title>Bootstrap</title><path fill="currentColor" d="M510 8a94.3 94.3 0 0 1 94 94v408a94.3 94.3 0 0 1-94 94H102a94.3 94.3 0 0 1-94-94V102a94.3 94.3 0 0 1 94-94h408m0-8H102C45.9 0 0 45.9 0 102v408c0 56.1 45.9 102 102 102h408c56.1 0 102-45.9 102-102V102C612 45.9 566.1 0 510 0z"/><path fill="currentColor" d="M196.77 471.5V154.43h124.15c54.27 0 91 31.64 91 79.1 0 33-24.17 63.72-54.71 69.21v1.76c43.07 5.49 70.75 35.82 70.75 78 0 55.81-40 89-107.45 89zm39.55-180.4h63.28c46.8 0 72.29-18.68 72.29-53 0-31.42-21.53-48.78-60-48.78h-75.57zm78.22 145.46c47.68 0 72.73-19.34 72.73-56s-25.93-55.37-76.46-55.37h-74.49v111.4z"/></svg>

_includes/icons/download.svg

+<svg xmlns="http://www.w3.org/2000/svg" focusable="false"{% if include.width %} width="{{ include.width }}"{% endif %}{% if include.height %} height="{{ include.height }}"{% endif %} fill="none" stroke="currentcolor" stroke-width="2"{% if include.class %} class="{{ include.class }}"{% endif %} viewBox="0 0 32 32" stroke-linecap="round" stroke-linejoin="round"><title>Download icon</title><path d="M9 22c-9 1-8-10 0-9C6 2 23 2 22 10c10-3 10 13 1 12m-12 4l5 4 5-4m-5-10v14"/></svg>

_includes/icons/import.svg

+<svg xmlns="http://www.w3.org/2000/svg" focusable="false"{% if include.width %} width="{{ include.width }}"{% endif %}{% if include.height %} height="{{ include.height }}"{% endif %} fill="none" stroke="currentcolor" stroke-width="2"{% if include.class %} class="{{ include.class }}"{% endif %} viewBox="0 0 32 32" stroke-linecap="round" stroke-linejoin="round"><title>Import icon</title><path d="M18 13l8-11L8 13l6 6-8 11 18-11z"/></svg>

_includes/icons/lightning.svg

+<svg xmlns="http://www.w3.org/2000/svg" focusable="false"{% if include.width %} width="{{ include.width }}"{% endif %}{% if include.height %} height="{{ include.height }}"{% endif %} fill="none" stroke="currentcolor" stroke-width="2"{% if include.class %} class="{{ include.class }}"{% endif %} viewBox="0 0 32 32" stroke-linecap="round" stroke-linejoin="round"><title>Lightning icon</title><path d="M18 13l8-11L8 13l6 6-8 11 18-11z"/></svg>

index.html

@@ -32,9 +32,7 @@ layout: home
 <div class="masthead-followup row m-0 border border-white">
   <div class="col-12 col-md-4 p-3 p-md-5 bg-light border border-white">
     <!-- Icon by Bytesize https://github.com/danklammer/bytesize-icons -->
-    <svg class="text-primary mb-2" viewBox="0 0 32 32" width="32" height="32" fill="none" stroke="currentcolor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2">
-      <path d="M28 22 L28 30 4 30 4 22 M16 4 L16 24 M8 16 L16 24 24 16" />
-    </svg>
+    {% include icons/import.svg width="32" height="32" class="text-primary mb-2" %}
     <h3>Installation</h3>
     <p>Include Bootstrap's source Sass and JavaScript files via Bower, Composer, Meteor, or npm. Package managed installs don't include documentation, but do include our build system and readme.</p>
 
@@ -55,9 +53,7 @@ bower install bootstrap#v{{ site.current_version }}
 
   <div class="col-12 col-md-4 p-3 p-md-5 bg-light border border-white">
     <!-- Icon by Bytesize https://github.com/danklammer/bytesize-icons -->
-    <svg class="text-primary mb-2" viewBox="0 0 32 32" width="32" height="32" fill="none" stroke="currentcolor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2">
-      <path d="M9 22 C0 23 1 12 9 13 6 2 23 2 22 10 32 7 32 23 23 22 M11 26 L16 30 21 26 M16 16 L16 30" />
-    </svg>
+    {% include icons/download.svg width="32" height="32" class="text-primary mb-2" %}
     <h3>Bootstrap CDN</h3>
     <p>When you only need to include Bootstrap's compiled CSS or JS, you can use the Bootstrap CDN.</p>
 
@@ -78,9 +74,7 @@ bower install bootstrap#v{{ site.current_version }}
 
   <div class="col-12 col-md-4 p-3 p-md-5 bg-light border border-white">
     <!-- Icon by Bytesize https://github.com/danklammer/bytesize-icons -->
-    <svg class="text-primary mb-2" viewBox="0 0 32 32" width="32" height="32" fill="none" stroke="currentcolor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2">
-      <path d="M18 13 L26 2 8 13 14 19 6 30 24 19 Z" />
-    </svg>
+    {% include icons/lightning.svg width="32" height="32" class="text-primary mb-2" %}
     <h3>Official Themes</h3>
     <p>
       Take Bootstrap 4 to the next level with official premium themes—toolkits built on Bootstrap with new components and plugins, docs, and build tools.