Prevent plugins from using core block namespaces

[nylen]

Fixes #333.

This PR prohibits plugins from registering blocks in the core or core-* namespaces (we currently use core-embed).

We should reserve these for future usage by core.

The PR works by setting an ALLOW_CORE_NAMESPACES flag when registering our core blocks, then unsetting it later. Because this flag is completely internal to the blocks module, it is not accessible by third-party code.

[codecov]

Codecov Report

Merging #2241 into master will increase coverage by 0.43%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2241      +/-   ##
==========================================
+ Coverage   24.23%   24.67%   +0.43%     
==========================================
  Files         142      143       +1     
  Lines        4460     4486      +26     
  Branches      756      757       +1     
==========================================
+ Hits         1081     1107      +26     
  Misses       2854     2854              
  Partials      525      525

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

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[youknowriad]

This should be way easier to do since we introduced the registerCoreBlocks function. Any plans on updating this, maybe we can take over @gziolo

[gziolo]

This should be way easier to do since we introduced the registerCoreBlocks function. Any plans on updating this, maybe we can take over @gziolo

Yes, it sounds like a great idea. We can enable such flag at the beginning registerCoreBlocks and disable at the end. It would allow adding additional logic which would be fully limited to the core blocks. 💯

[gziolo]

Let's close it and implement it as part of #4841. Most likely it will have to be done on PHP side.