Editor: Improves layout block support in wp_get_layout_style().
This commit merges the remaining changes from Gutenberg PR 40875. It's Part 2 (see [54162] for Part 1) of a layout improvement initiative and targets wp_get_layout_style() in layout.php.
Context:
The overall initiative is to improve layout block support:
to use centralised layout definitions, output base layout styles from global styles, introduce a layout type semantic classname, reduce duplication of container class and style tag output, and fix blockGap at the block level in global styles.
Changes include:
- Adding an optional parameter
$block_spacing to wp_get_layout_style() for setting a custom spacing on the block.
- Adding handle for the block spacing.
- Using the style engine to to enqueue and render layout styles via
wp_style_engine_get_stylesheet_from_css_rules().
- Introduces a new test file for
wp_get_layout_style().
Follow-up to [54162], [54160], [54159], [53421], [52380], [53085], [52069].
Props andrewserong, isabel_brison, costdev, hellofromTonya.
See #56467.