Refine UI for FTP modal and shiny updates

Numerous changes to make the FTP modal experience a good one.  These include:
 * Update HTML used by both the form here and the form on the standalone screen
 * Allow users to cancel FTP install
 * Focus locking in the modal
 * Focus on modal form on load
 * ARIA Attributes
 * Style Enhancements
 * Add low screen height (such as phone and some tablets) friendly experience for entering credentials

Props ericlewis, afercia 
Fixes #31608



git-svn-id: https://develop.svn.wordpress.org/trunk@31949 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/script-loader.php

@@ -529,6 +529,7 @@ function wp_default_scripts( &$scripts ) {
 				'updateFailed'  => __( 'Update failed.' ),
 				'updatingMsg'   => __( 'Updating... please wait.' ),
 				'updatedMsg'    => __( 'Update completed successfully.' ),
+				'updateCancel'  => __( 'Update canceled' ),
 			)
 		) );