I18N: Improve translator comments.

* Add missing translator comments.
* Fix placement of some translator comments. Translator comments should be on the line directly above the line containing the translation function call for optimal compatibility with various `.pot` file generation tools. The CS auto-fixing, which changed some inconsistent function calls to multi-line function calls, is part of the reason why this was no longer the case for a select group of translator comments.

Includes minor code layout fixes.

Polyglots, rejoice! All WordPress core files now have translator comments for all strings with placeholders!

Props jrf, subrataemfluence, GaryJ, webdados, Dency, swissspidy, alvarogois, marcomartins, mihaiiceyro, vladwtz, niq1982, flipkeijzer, michielatyoast, chandrapatel, thrijith, joshuanoyce, FesoVik, tessak22, bhaktirajdev, cleancoded, dhavalkasvala, garrett-eclipse, bibliofille, socalchristina, priyankkpatel, 5hel2l2y, adamsilverstein, JeffPaul, pierlo, SergeyBiryukov.
Fixes #44360.

git-svn-id: https://develop.svn.wordpress.org/trunk@45926 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-custom-background.php

@@ -229,10 +229,11 @@ class Custom_Background {
 <div class="notice notice-info hide-if-no-customize">
 	<p>
 			<?php
-				printf(
-					__( 'You can now manage and live-preview Custom Backgrounds in the <a href="%1$s">Customizer</a>.' ),
-					admin_url( 'customize.php?autofocus[control]=background_image' )
-				);
+			printf(
+				/* translators: %s: URL to background image configuration in Customizer */
+				__( 'You can now manage and live-preview Custom Backgrounds in the <a href="%s">Customizer</a>.' ),
+				admin_url( 'customize.php?autofocus[control]=background_image' )
+			);
 			?>
 	</p>
 </div>
@@ -240,7 +241,12 @@ class Custom_Background {
 
 		<?php if ( ! empty( $this->updated ) ) { ?>
 <div id="message" class="updated">
-<p><?php printf( __( 'Background updated. <a href="%s">Visit your site</a> to see how it looks.' ), home_url( '/' ) ); ?></p>
+	<p>
+			<?php
+			/* translators: %s: Home URL */
+			printf( __( 'Background updated. <a href="%s">Visit your site</a> to see how it looks.' ), home_url( '/' ) );
+			?>
+	</p>
 </div>
 		<?php } ?>