Administration: Remove empty form action attributes.

Remove the `action` attribute in the login language selector, privacy forms, and classic widget forms.

An empty `action` attribute is invalid HTML4 and unsupported HTML5. The `action` attribute is optional, but must have a valid URL when provided.

Props Malae, audrasjb, bartkleinreesink, nicolefurlan, shubhamsedani, costdev, peterwilsoncc, rajinsharwar, joedolson.
Fixes #58226.

git-svn-id: https://develop.svn.wordpress.org/trunk@57295 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/options-privacy.php

@@ -270,7 +270,7 @@ wp_admin_notice(
 				</label>
 			</th>
 			<td>
-				<form class="wp-create-privacy-page" method="post" action="">
+				<form class="wp-create-privacy-page" method="post">
 					<input type="hidden" name="action" value="create-privacy-page" />
 					<?php
 					wp_nonce_field( 'create-privacy-page' );
@@ -293,7 +293,7 @@ wp_admin_notice(
 				</label>
 			</th>
 			<td>
-				<form method="post" action="">
+				<form method="post">
 					<input type="hidden" name="action" value="set-privacy-page" />
 					<?php
 					wp_dropdown_pages(

src/wp-admin/widgets-form.php

@@ -478,7 +478,7 @@ foreach ( $wp_registered_sidebars as $sidebar => $registered_sidebar ) {
 
 				<?php if ( $is_inactive_widgets ) { ?>
 				<div class="remove-inactive-widgets">
-					<form action="" method="post">
+					<form method="post">
 						<p>
 							<?php
 							$attributes = array( 'id' => 'inactive-widgets-control-remove' );

src/wp-login.php

@@ -364,7 +364,7 @@ function login_footer( $input_id = '' ) {
 		if ( ! empty( $languages ) ) {
 			?>
 			<div class="language-switcher">
-				<form id="language-switcher" action="" method="get">
+				<form id="language-switcher" method="get">
 
 					<label for="language-switcher-locales">
 						<span class="dashicons dashicons-translation" aria-hidden="true"></span>