Editor: Reduce the use of the _wp_array_get() function to improve performance.

`_wp_array_get()` is an expensive function, and it's called thousands of times on each page view on the front end. While the function performance was slightly improved in #58376, it is still called more times than it should be.

This commit aims to further optimize its usage:
* In many cases, `_wp_array_get()` can be replaced with a much simpler and faster `isset()` check.
* The `isset()` function is capable of checking nested arrays, so `isset( $foo['a']['b']['c'] )` will return false even if `$foo['a']` is unset, without throwing any errors or warnings.
* When `_wp_array_get()` cannot be directly replaced with `isset()`, it would be good practice to wrap it in an `isset()` function so that `_wp_array_get()` only runs when it needs to.

Original PR from Gutenberg repository:
* [https://github.com/WordPress/gutenberg/pull/51116 #51116 Performance improvement: Reduce the use of the _wp_array_get() function]

Follow-up to [55851], [56382].

Props aristath, jrf, spacedmonkey, mukesh27, swissspidy, hellofromTonya.
Fixes #59405.
Built from https://develop.svn.wordpress.org/trunk@56709


git-svn-id: http://core.svn.wordpress.org/trunk@56221 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/blocks.php

@@ -1636,7 +1636,7 @@ function wp_migrate_old_typography_shape( $metadata ) {
 	);
 
 	foreach ( $typography_keys as $typography_key ) {
-		$support_for_key = _wp_array_get( $metadata['supports'], array( $typography_key ), null );
+		$support_for_key = isset( $metadata['supports'][ $typography_key ] ) ? $metadata['supports'][ $typography_key ] : null;
 
 		if ( null !== $support_for_key ) {
 			_doing_it_wrong(