Widgets: Replace http with https in the link placeholder widget image

The existing placeholder can make the user think that they must use http. We should encourage the use of https. 
Also, the block editor uses https for its placeholders. Let's add some consistency.

Props Chaton666, audrasjb, mukesh27.
Fixes #46320.

Built from https://develop.svn.wordpress.org/trunk@45777


git-svn-id: http://core.svn.wordpress.org/trunk@45588 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45776';
+$wp_version = '5.3-alpha-45777';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/widgets/class-wp-widget-media-image.php

@@ -335,7 +335,7 @@ class WP_Widget_Media_Image extends WP_Widget_Media {
 			<# if ( data.url ) { #>
 			<p class="media-widget-image-link">
 				<label for="{{ elementIdPrefix }}linkUrl"><?php esc_html_e( 'Link to:' ); ?></label>
-				<input id="{{ elementIdPrefix }}linkUrl" type="text" class="widefat link" value="{{ data.link_url }}" placeholder="http://" pattern="((\w+:)?\/\/\w.*|\w+:(?!\/\/$)|\/|\?|#).*">
+				<input id="{{ elementIdPrefix }}linkUrl" type="text" class="widefat link" value="{{ data.link_url }}" placeholder="https://" pattern="((\w+:)?\/\/\w.*|\w+:(?!\/\/$)|\/|\?|#).*">
 			</p>
 			<# } #>
 		</script>