Schema Compare extension (#4974)

* extension now working

* fix diff editor title disappearing and remove border from source and target name boxes

* redoing a bunch of stuff that disappeared after rebasing

* add images and add to extensions.ts

* moving a few changes to the right place after rebase

* formatting

* update toolbar svgs

* addressing comments

* add return types

* Adding PR comments

* Adding light and dark theme icons

* Fixing the diff editor title for dark theme

build/lib/extensions.ts

@@ -300,7 +300,8 @@ const sqlBuiltInExtensions = [
 	'profiler',
 	'admin-pack',
 	'big-data-cluster',
-	'dacpac'
+	'dacpac',
+	'schema-compare'
 ];
 // {{SQL CARBON EDIT}} - End