Extends the REST API endpoint for block patterns to provide a source attribute that can be used to filter patterns. Props aaronrobertshaw, mukesh27, talldanwp, ramonopoly. Fixes 58622. Built from https://develop.svn.wordpress.org/trunk@56063 git-svn-id: http://core.svn.wordpress.org/trunk@55575 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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