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

src/sql/sqlops.proposed.d.ts

@@ -1602,6 +1602,7 @@ declare module 'sqlops' {
 		AgentServicesProvider = 'AgentServicesProvider',
 		CapabilitiesProvider = 'CapabilitiesProvider',
 		DacFxServicesProvider = 'DacFxServicesProvider',
+		SchemaCompareServicesProvider = 'SchemaCompareServicesProvider',
 		ObjectExplorerNodeProvider = 'ObjectExplorerNodeProvider'
 	}