Remove global h2 css rule in favour of heading styles/components (#32969)

* Remove global h2 css rule in favour of heading styles/components

* Use Compound Heading in shared-components

and forbid hX elements

* Use Compound Heading in settings

add back margin to some legacy headings

* Tweak some headings

* Update screenshots

* Update screenshots

* Update snapshots

* Tweak .gitignore

* Update snapshots

* Iterate

* Update screenshots

* Update screenshots

* Update screenshot

apps/web/res/css/views/dialogs/_DevtoolsDialog.pcss

@@ -30,8 +30,7 @@ Please see LICENSE files in the repository root for full details.
 
 .mx_DevTools_toolHeading {
     color: var(--cpd-color-text-secondary);
-    font-weight: var(--cpd-font-weight-semibold);
-    font-size: var(--cpd-font-size-heading-sm);
+    font: var(--cpd-font-heading-sm-semibold);
 }
 
 .mx_DevTools_content {