Add CSS cascade layers for Compound, shared components, and app/web styles (#33302)

* Layer Compound and shared component CSS

* Layer app theme CSS

* Remove !important flags from ActionBarView

* Remove unnecessary !important statements from shared components

* Avoid dead code errors for *.pcss just because layer is specified after @import url

* Remove unnecessary !important styling

* Override Banner defaults in RoomStatusBarView

* Updated snaps

* Updated snaps

* Fix styling of media body in app/web

* Fix styling for Compound anchors

* Fix styling issues in app/web

* More styling fixes

* Fix a problem extracting css for HTMLExport

* Revert changes

* Fix for theme styling

* Add test to improve coverage

* Prettier

* Fix styling issues

* Add data-kind attribute to avoid global styling override

* Update screenshot that now is correct

* Revert data-kind attribute

* Handle LinkPreview styling in .pcss

* Fix flaky test: Avoid racing the lazy-loaded ManageEventIndexDialog

* Take care of review comments

* Updated snaps

* Updated snaps again after merge

* Remove !important from RoomStatusBar

apps/web/res/css/views/messages/_MFileBody.pcss

@@ -7,7 +7,6 @@ Please see LICENSE files in the repository root for full details.
 */
 
 .mx_MFileBody [data-type="download"] {
-    color: $accent;
     height: var(--cpd-space-9x);
 
     & object {

apps/web/res/css/views/messages/_MediaBody.pcss

@@ -17,6 +17,8 @@ Please see LICENSE files in the repository root for full details.
     color: $secondary-content;
     font: var(--cpd-font-body-md-regular);
     line-height: $font-24px;
+}
 
-    padding: 6px 12px;
+.mx_MAudioBody > .mx_MediaBody {
+    border-radius: var(--MBody-border-radius);
 }

apps/web/res/css/views/messages/_TextualEvent.pcss

@@ -19,3 +19,12 @@ Please see LICENSE files in the repository root for full details.
         opacity: unset; /* Unset the opacity value specified above on the search results panel */
     }
 }
+
+.mx_TextualBody_urlPreviews {
+    /* Let shared-components own preview link colours instead of the app-wide anchor colour. */
+    a:where(:not([data-kind])):hover,
+    a:where(:not([data-kind])):link,
+    a:where(:not([data-kind])):visited {
+        color: revert-layer;
+    }
+}