Filter image_hwstring()

[wpsmith]

Make it possible to remove width and height from media HTML output functions by filtering image_hwstring(). This is perfect for responsiveness.

This can be done a few different ways:

function image_hwstring($width, $height) {
	$out = '';
	if ($width)
		$out .= 'width="'.intval($width).'" ';
	if ($height)
		$out .= 'height="'.intval($height).'" ';
	return apply_filters( 'image_hwstring', $out );
}

This could be easily filtered by something like:
add_filter( 'image_hwstring', 'return_empty_string' );

See #20357.

I think image_hwstring() is too low level for this, as it is but a helper.

Instead, we should push 'height' and 'width' into the attributes in wp_get_attachment_image(), which will force them through the wp_get_attachment_image_attributes filter. There is a duplicate ticket covering thid.

#14110

#22285 was marked as a duplicate.