Add WP_XML_Tag_Processor and WP_XML_Processor #6372

Job	Run time
Core running from build / Core running from build / Linux	2m 20s
Core running from src / Core running from src / Linux	1m 58s
Core running from build / Core running from build / Windows	3m 44s
Core running from src / Core running from src / Windows	5m 45s
Core running from src / Core running from src / MacOS	1m 50s
Core running from build / Core running from build / MacOS	2m 6s
Gutenberg running from build / Gutenberg running from build / Linux	8m 41s
Gutenberg running from src / Gutenberg running from src / Linux	8m 41s
Gutenberg running from build / Gutenberg running from build / Windows	12m 31s
Gutenberg running from src / Gutenberg running from src / Windows	12m 10s
Gutenberg running from build / Gutenberg running from build / MacOS	7m 1s
Gutenberg running from src / Gutenberg running from src / MacOS	8m 35s
Slack Notifications	0s
Failed workflow tasks	0s
	1h 15m 22s

Provide feedback