Editor: Move printing TinyMCE scripts into an action

Moving this logic into an action allows plugins to override
how/when TinyMCE is loaded. Specifically, Gutenberg needs to
be able to prevent TinyMCE scripts from being written into
the page when TinyMCE should be loaded asynchronously when it
is actually needed.

src/wp-includes/class-wp-editor.php

@@ -1556,9 +1556,7 @@ public static function print_tinymce_scripts() {
 			script_concat_settings();
 		}
 
-		wp_print_scripts( array( 'wp-tinymce' ) );
-
-		echo "<script type='text/javascript'>\n" . self::wp_mce_translation() . "</script>\n";
+		do_action( 'print_tinymce_scripts' );
 	}
 
 	/**

src/wp-includes/script-loader.php

@@ -63,6 +63,25 @@ function wp_register_tinymce_scripts( $scripts, $force_uncompressed = false ) {
 	$scripts->add( 'wp-tinymce-lists', includes_url( "js/tinymce/plugins/lists/plugin$suffix.js" ), array( 'wp-tinymce' ), $tinymce_version );
 }
 
+/**
+ * Function responsible for printing the TinyMCE scripts.
+ *
+ * @since 5.4.0
+ */
+function wp_print_tinymce_scripts() {
+	wp_print_scripts( array( 'wp-tinymce' ) );
+
+	echo "<script type='text/javascript'>\n" . _WP_Editors::wp_mce_translation() . "</script>\n";
+}
+
+/**
+ * Executed in _WP_Editors::print_tinymce_scripts
+ * after concatenation settings have been initialized.
+ *
+ * @see _WP_Editors::print_tinymce_scripts()
+ */
+add_action( 'print_tinymce_scripts', 'wp_print_tinymce_scripts' );
+
 /**
  * Registers all the WordPress vendor scripts that are in the standardized
  * `js/dist/vendor/` location.

tests/phpunit/tests/editor/wpEditors.php

@@ -91,4 +91,12 @@ public function test_wp_link_query_returns_filtered_search_results() {
 			$actual
 		);
 	}
+
+	public function test_print_tinymce_scripts_calls_print_tinymce_scripts_action() {
+		$this->assertEquals( 0, did_action( 'print_tinymce_scripts' ) );
+
+		_WP_Editors::print_tinymce_scripts();
+
+		$this->assertEquals( 1, did_action( 'print_tinymce_scripts' ) );
+	}
 }