HTML API: Introduce safe HTML templating. #1869

Job	Run time
Core running from src / Core running from src / Linux	2m 9s
Core running from build / Core running from build / Linux	2m 0s
Core running from src / Core running from src / Windows	3m 8s
Core running from build / Core running from build / Windows	3m 27s
Core running from build / Core running from build / MacOS	3m 30s
Core running from src / Core running from src / MacOS	3m 36s
Gutenberg running from build / Gutenberg running from build / Linux	9m 3s
Gutenberg running from src / Gutenberg running from src / Linux	8m 52s
Gutenberg running from build / Gutenberg running from build / Windows	12m 22s
Gutenberg running from src / Gutenberg running from src / Windows	11m 57s
Gutenberg running from build / Gutenberg running from build / MacOS	17m 29s
Gutenberg running from src / Gutenberg running from src / MacOS	19m 5s
Leave WordPress Playground details	3s
Slack Notifications	0s
Failed workflow tasks	0s
	1h 36m 41s

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