Bump version to 5.0.0-alpha1 (#29925)

Also add v4.5.0 in versions and keep README.md pointing to v4.5.0 so that there are no broken stuff.

site/content/docs/5.0/utilities/visibility.md

@@ -0,0 +1,25 @@
+---
+layout: docs
+title: Visibility
+description: Control the visibility, without modifying the display, of elements with visibility utilities.
+group: utilities
+---
+
+Set the `visibility` of elements with our visibility utilities. These utility classes do not modify the `display` value at all and do not affect layout – `.invisible` elements still take up space in the page. Content will be hidden both visually and for assistive technology/screen reader users.
+
+Apply `.visible` or `.invisible` as needed.
+
+{{< highlight html >}}
+<div class="visible">...</div>
+<div class="invisible">...</div>
+{{< /highlight >}}
+
+{{< highlight scss >}}
+// Class
+.visible {
+  visibility: visible !important;
+}
+.invisible {
+  visibility: hidden !important;
+}
+{{< /highlight >}}