Add explanation to mute dialog, refactor and clean up mute/block UI (#11992)

* Add some explanation to the mute modal dialog

* Remove `isSubmitting` from mute modal code, this wasn't used

* Refactor block modal

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

* Refactor SCSS a bit

* Put mute modal toggle to the same side as in the report dialog for consistency

* Reword mute explanation

* Fix mute explanation styling

* Left-align all text in mute confirmation modal

app/javascript/mastodon/features/ui/components/modal_root.js

@@ -13,6 +13,7 @@ import ConfirmationModal from './confirmation_modal';
 import FocalPointModal from './focal_point_modal';
 import {
   MuteModal,
+  BlockModal,
   ReportModal,
   EmbedModal,
   ListEditor,
@@ -25,6 +26,7 @@ const MODAL_COMPONENTS = {
   'BOOST': () => Promise.resolve({ default: BoostModal }),
   'CONFIRM': () => Promise.resolve({ default: ConfirmationModal }),
   'MUTE': MuteModal,
+  'BLOCK': BlockModal,
   'REPORT': ReportModal,
   'ACTIONS': () => Promise.resolve({ default: ActionsModal }),
   'EMBED': EmbedModal,