Refactor style properties computation in WP Theme JSON class #6958

Job	Run time
Core running from build / Core running from build / Linux	2m 0s
Core running from src / Core running from src / Linux	1m 53s
Core running from build / Core running from build / Windows	4m 9s
Core running from src / Core running from src / Windows	4m 36s
Core running from build / Core running from build / MacOS	1m 39s
Core running from src / Core running from src / MacOS	1m 35s
Gutenberg running from build / Gutenberg running from build / Linux	8m 31s
Gutenberg running from src / Gutenberg running from src / Linux	8m 36s
Gutenberg running from build / Gutenberg running from build / Windows	11m 8s
Gutenberg running from src / Gutenberg running from src / Windows	12m 2s
Gutenberg running from build / Gutenberg running from build / MacOS	7m 48s
Gutenberg running from src / Gutenberg running from src / MacOS	10m 2s
Slack Notifications	0s
Failed workflow tasks	0s
	1h 13m 59s

Provide feedback