Accessibility: Media: Add a "Copy URL" button to the attachment File URL fields.

For a number of years, various screens in the WordPress admin provided users with a readonly input field to copy the attachment file URL. Manually copying from a readonly field is an annoying task at best even for mouser users. It's a usability and accessibility issue at the same time. 
These fields now have a new "Copy URL" button that is easy to use and accessible to everyone.

Props theolg, markdubois, vabrashev, sajjad67, xkon, nrqsnchz, melchoyce, audrasjb, afercia.
See #41612, #50322, #50335.
Fixes #48463.


git-svn-id: https://develop.svn.wordpress.org/trunk@48232 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/media.css

@@ -797,6 +797,16 @@ border color while dragging a file over the uploader drop area */
 	text-decoration: none;
 }
 
+.copy-to-clipboard-container {
+	display: flex;
+	align-items: center;
+	margin-top: 8px;
+	clear: both;
+}
+
+.copy-to-clipboard-container .success {
+	margin-left: 8px;
+}
 
 /*------------------------------------------------------------------------------
   14.2 - Image Editor
@@ -1215,6 +1225,10 @@ audio, video {
 		width: auto;
 		max-width: none;
 	}
+
+	.copy-to-clipboard-container .success {
+		font-size: 14px;
+	}
 }
 
 /**

src/wp-admin/includes/media.php

@@ -3268,6 +3268,10 @@ function attachment_submitbox_metadata() {
 	<div class="misc-pub-section misc-pub-attachment">
 		<label for="attachment_url"><?php _e( 'File URL:' ); ?></label>
 		<input type="text" class="widefat urlfield" readonly="readonly" name="attachment_url" id="attachment_url" value="<?php echo esc_attr( $att_url ); ?>" />
+		<span class="copy-to-clipboard-container">
+			<button type="button" class="button copy-attachment-url edit-media" data-clipboard-target="#attachment_url"><?php _e( 'Copy URL' ); ?></button>
+			<span class="success hidden" aria-hidden="true"><?php _e( 'Copied!' ); ?></span>
+		</span>
 	</div>
 	<div class="misc-pub-section misc-pub-filename">
 		<?php _e( 'File name:' ); ?> <strong><?php echo $filename; ?></strong>