Screen Options: Improve items per page option label.

Previously the label just said "Posts", "Pages", or "Comments". This was bad in terms of accessibility and internationalization because of missing context.
This change adds a default label "Number of items per page:" to `WP_Screen->render_per_page_options()` and removes all the existing one-word labels.

props afercia.
fixes #31349, #15576.
Built from https://develop.svn.wordpress.org/trunk@31696


git-svn-id: http://core.svn.wordpress.org/trunk@31677 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/common-rtl.css

@@ -1506,6 +1506,26 @@ form.upgrade .hint {
 	display: none;
 }
 
+.metabox-prefs .screen-options {
+	padding-top: 10px;
+}
+
+.metabox-prefs .screen-options input,
+.metabox-prefs .screen-options label {
+	margin-top: 0;
+	margin-bottom: 0;
+	vertical-align: middle;
+}
+
+.metabox-prefs .screen-options .screen-per-page {
+	margin-left: 15px;
+}
+
+.metabox-prefs .screen-options label {
+	line-height: 28px;
+	padding-left: 0;
+}
+
 /*------------------------------------------------------------------------------
   6.2 - Help Menu
 ------------------------------------------------------------------------------*/

wp-admin/css/common.css

@@ -1506,6 +1506,26 @@ form.upgrade .hint {
 	display: none;
 }
 
+.metabox-prefs .screen-options {
+	padding-top: 10px;
+}
+
+.metabox-prefs .screen-options input,
+.metabox-prefs .screen-options label {
+	margin-top: 0;
+	margin-bottom: 0;
+	vertical-align: middle;
+}
+
+.metabox-prefs .screen-options .screen-per-page {
+	margin-right: 15px;
+}
+
+.metabox-prefs .screen-options label {
+	line-height: 28px;
+	padding-right: 0;
+}
+
 /*------------------------------------------------------------------------------
   6.2 - Help Menu
 ------------------------------------------------------------------------------*/