Trac 56780: block_template_part test cases

masthead.html

<!-- wp:group {"tagName":"header","layout":{"type":"flex","flexWrap":"wrap"}} -->
<header id="masthead" class="wp-block-group" style="display: block;">
	<h2>masthead.html</h2>
	<h4>wptexturize</h4>
	<p>'cause today's effort makes it worth tomorrow's "holiday"...</p>
	<h4>convert_smilies</h4>
	<p>:)</p>
	<h4>shortcode_unautop (shortcode wrapped in paragraph)</h4>
	<p>[hello_world]</p>
	<h4>wp_filter_content_tags</h4>
	<img width="408" height="287" src="https://placekitten.com/408/287">
	<h4>do_shortcode</h4>
	<!-- wp:shortcode -->
	[hello_world]
	<!-- /wp:shortcode -->
	<h4>$wp_embed->autoembed</h4>
	https://youtube.com/shorts/_H4vwkGvWjE?feature=share

	<h4>testing notes</h4>
	<p><em>note: paragraphs in <code>#masthead</code> are styled with bg and border for visibility</em></p>
	<style>
		#masthead p { background: #f5f5f5; border: 1px blue solid; margin: 1px; }
		#masthead { padding: 1em; }
		#masthead h2 { margin-bottom: 1em; }
		#masthead h4 { margin-top: .5em; }
	</style>
</header>
<!--  /wp:group -->