Style theme variations: add property extraction and merge utils (#58803)

* First commit

Pulling out the utils from #56622 so we test separately

* Adding failing tests :)

* Adds working tests
Removes extra functions - now internal to the hook

* Adds more tests

* Adds filterObjectByProperty tests

* Update packages/edit-site/src/hooks/use-theme-style-variations/use-theme-style-variations-by-property.js

Co-authored-by: Andrew Serong <14988353+andrewserong@users.noreply.github.com>

* Merge map callbacks

* More tests, adding a `null` check too

* Update comment to reflect functionality

* Update test to ensure we don't reference original object

---------

Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>
Co-authored-by: andrewserong <andrewserong@git.wordpress.org>
Co-authored-by: scruffian <scruffian@git.wordpress.org>

packages/edit-site/src/hooks/push-changes-to-global-styles/index.js

@@ -26,6 +26,7 @@ import { store as coreStore } from '@wordpress/core-data';
  */
 import { useSupportedStyles } from '../../components/global-styles/hooks';
 import { unlock } from '../../lock-unlock';
+import cloneDeep from '../../utils/clone-deep';
 
 const { cleanEmptyObject, GlobalStylesContext } = unlock(
 	blockEditorPrivateApis
@@ -275,10 +276,6 @@ function setNestedValue( object, path, value ) {
 	return object;
 }
 
-function cloneDeep( object ) {
-	return ! object ? {} : JSON.parse( JSON.stringify( object ) );
-}
-
 function PushChangesToGlobalStylesControl( {
 	name,
 	attributes,