Editor: Introduce new API method that register block from block.json
metadata file
Backports changes added to Gutenberg in:
- https://github.com/WordPress/gutenberg/pull/20794
- https://github.com/WordPress/gutenberg/pull/22519
`register_block_type_from_metadata` function is going to be used to register all blocks on the server using `block.json` metadata files.
Props ocean90, azaozz, aduth, mcsf, jorgefilipecosta, spacedmonkey, nosolosw, swissspidy and noahtallen.
Fixes #50263.
git-svn-id: https://develop.svn.wordpress.org/trunk@48141 602fd350-edb4-49c9-b593-d223f7449a82