uploads: allow changing thumbnail size on My Uploads / All Uploads pages.

* Add a "Size" menu to the My Uploads / All Uploads pages to allow
  changing the thumbnail size.
* Make the My Uploads / All Uploads pages use the same thumbnail size as
  the post index page.
* Change the "Gallery | Table" links on the My Uploads page to icons.

app/components/preview_size_menu_component.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+# The dropdown menu for selecting the thumbnail size. Used on the post index
+# page, the upload index page, and the media assets index page.
+class PreviewSizeMenuComponent < ApplicationComponent
+  attr_reader :current_size
+
+  def initialize(current_size:)
+    @current_size = current_size.to_i
+  end
+end