Block Themes should now use the following folders:
- templates instead of block-templates
- parts instead of block-template-parts
Existing themes and folders will continue to work without impact.
Props bernhard-reiter.
Fixes#54493.
git-svn-id: https://develop.svn.wordpress.org/trunk@52247 602fd350-edb4-49c9-b593-d223f7449a82