Refactor style properties computation in WP Theme JSON class #6938

Job	Run time
Core running from build / Core running from build / Linux	2m 6s
Core running from src / Core running from src / Linux	1m 52s
Core running from build / Core running from build / Windows	3m 55s
Core running from src / Core running from src / Windows	3m 20s
Core running from build / Core running from build / MacOS	1m 37s
Core running from src / Core running from src / MacOS	1m 34s
Gutenberg running from build / Gutenberg running from build / Linux	8m 29s
Gutenberg running from src / Gutenberg running from src / Linux	7m 49s
Gutenberg running from build / Gutenberg running from build / Windows	11m 9s
Gutenberg running from src / Gutenberg running from src / Windows	12m 12s
Gutenberg running from build / Gutenberg running from build / MacOS	6m 17s
Gutenberg running from src / Gutenberg running from src / MacOS	8m 6s
Slack Notifications	0s
Failed workflow tasks	0s
	1h 8m 26s

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