I18N: Provide gettext context to disambiguate various translation strings.

This changeset adds context to various strings:
- `'Background'` string when referring to Custom Background appearance screens
- `'Header'` string when referring to Custom Header appearance screens
- `'General'`, `'Header'` and `'Footer'` strings when referring to template part areas

Props gonzomir, SergeyBiryukov, mukesh27, costdev, ankitmaru.
Fixes #58424.



git-svn-id: https://develop.svn.wordpress.org/trunk@55881 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/block-template-utils.php

@@ -65,7 +65,7 @@ function get_allowed_block_template_part_areas() {
 	$default_area_definitions = array(
 		array(
 			'area'        => WP_TEMPLATE_PART_AREA_UNCATEGORIZED,
-			'label'       => __( 'General' ),
+			'label'       => _x( 'General', 'template part area' ),
 			'description' => __(
 				'General templates often perform a specific role like displaying post content, and are not tied to any particular area.'
 			),
@@ -74,7 +74,7 @@ function get_allowed_block_template_part_areas() {
 		),
 		array(
 			'area'        => WP_TEMPLATE_PART_AREA_HEADER,
-			'label'       => __( 'Header' ),
+			'label'       => _x( 'Header', 'template part area' ),
 			'description' => __(
 				'The Header template defines a page area that typically contains a title, logo, and main navigation.'
 			),
@@ -83,7 +83,7 @@ function get_allowed_block_template_part_areas() {
 		),
 		array(
 			'area'        => WP_TEMPLATE_PART_AREA_FOOTER,
-			'label'       => __( 'Footer' ),
+			'label'       => _x( 'Footer', 'template part area' ),
 			'description' => __(
 				'The Footer template defines a page area that typically contains site credits, social links, or any other combination of blocks.'
 			),