Posts, Post Types: Introduce "Filter by date" and "Filter by category" as post type and taxonomy labels, respectively.

This provides a more consistent location for these strings and allows for reusing them in other places without hardcoding them in the markup.

Props nicolalaserra, audrasjb, johnjamesjacoby, SergeyBiryukov.
Fixes #42421.

git-svn-id: https://develop.svn.wordpress.org/trunk@50120 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-posts-list-table.php

@@ -456,7 +456,8 @@ class WP_Posts_List_Table extends WP_List_Table {
 				'selected'        => $cat,
 			);
 
-			echo '<label class="screen-reader-text" for="cat">' . __( 'Filter by category' ) . '</label>';
+			echo '<label class="screen-reader-text" for="cat">' . get_taxonomy( 'category' )->labels->filter_by_item . '</label>';
+
 			wp_dropdown_categories( $dropdown_options );
 		}
 	}