Embeds: adjust ordering to better reflect usage.

[mtias]

This is a very minimal and low effort step towards better organizing embeds without making any bigger changes.

See #2120.

[codecov]

Codecov Report

Merging #2175 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #2175   +/-   ##
=======================================
  Coverage   22.15%   22.15%           
=======================================
  Files         138      138           
  Lines        4283     4283           
  Branches      723      723           
=======================================
  Hits          949      949           
  Misses       2814     2814           
  Partials      520      520

Impacted Files	Coverage Δ
blocks/library/embed/index.js	45.97% <100%> (ø)	⬆️

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[aduth]

As far as reviewing these sorts of changes, it would be easier if the variants were defined as triples to loop over:

[
	[ 'core/embed', 'Embed', 'video-alt3' ],
	[ 'core-embed/twitter', 'Twitter', 'twitter' ],
	// ...
].forEach( ( [ blockName, title, icon ] ) => {
	registerBlockType(
		blockName,
		getEmbedBlockSettings( {
			title,
			icon,
		} )
	);
} );

[mtias]

@aduth I like that, we would also want to allow aliases like "tweet" for twitter.