Use a switch to toggle proposal selection

The button to select/deselect a proposal wasn't very intuitive; for
example, it wasn't obvious that pressing a button saying "selected"
would deselect the proposal.

So we're using a switch control, like we do to enable/disable features
since commit fabe97e50.

app/components/admin/proposals/toggle_selection_component.html.erb

@@ -1 +1 @@
-<%= button_to text, path, options %>
+<%= render Admin::ToggleSwitchComponent.new(action, proposal, pressed: selected?, **options) %>

app/components/admin/proposals/toggle_selection_component.rb

@@ -7,27 +7,21 @@ class Admin::Proposals::ToggleSelectionComponent < ApplicationComponent
 
   private
 
-    def text
-      if proposal.selected?
-        t("admin.proposals.index.selected")
-      else
-        t("admin.proposals.index.select")
-      end
+    def action
+      :toggle_selection
     end
 
-    def path
-      admin_polymorphic_path(proposal, action: :toggle_selection)
+    def selected?
+      proposal.selected?
     end
 
     def options
-      { remote: true, method: :patch, class: html_class }
+      {
+        "aria-label": label
+      }
     end
 
-    def html_class
-      if proposal.selected?
-        "button expanded"
-      else
-        "button hollow expanded"
-      end
+    def label
+      t("admin.actions.label", action: t("admin.actions.select"), name: proposal.title)
     end
 end