…mpiling the styles.

In layout.php, if there is no block-level value for blockGap, but a global styles value available for blockGap, use the latter.

In layout.php, move check for global style into gutenberg_render_layout_support_flag

- Before we were unsetting blockGap for block and elements from the merged $theme_json structure in sanitize().
- After we keep them in the merged $theme_json, but skip them when printing out the global stylesheet.

…on in #40952