Blocks: Fix meta attributes selector not returning the correct value if edited

[youknowriad]

I think the editor's state has been refactored at some point which introduced this regression. This is probably worth a unit test but I have to go to WCUS right now. Feel free to add it if possible.

Testing instructions

• Add a block with a "meta" attribute
• Try to update the value
• The value should update as soon as you type.

[codecov]

Codecov Report

Merging #3754 into master will increase coverage by 2.37%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3754      +/-   ##
==========================================
+ Coverage   37.67%   40.04%   +2.37%     
==========================================
  Files         279      279              
  Lines        6737     7179     +442     
  Branches     1226     1369     +143     
==========================================
+ Hits         2538     2875     +337     
- Misses       3538     3615      +77     
- Partials      661      689      +28

Impacted Files	Coverage Δ
editor/selectors.js	93.54% <100%> (+0.08%)	⬆️
editor/store.js	81.81% <0%> (-1.52%)	⬇️
editor/components/block-list/block.js	1.86% <0%> (-0.38%)	⬇️
editor/store-defaults.js	100% <0%> (ø)	⬆️
blocks/api/raw-handling/test/integration/index.js	100% <0%> (ø)	⬆️
blocks/hooks/index.js	100% <0%> (ø)	⬆️
blocks/api/registration.js	100% <0%> (ø)	⬆️
blocks/block-edit/index.js	100% <0%> (ø)	⬆️
components/higher-order/with-api-data/index.js	84.33% <0%> (+0.58%)	⬆️
... and 4 more

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[mcsf]

The fix is good.

I think the editor's state has been refactored at some point which introduced this regression.

Yes, I believe in 2c0ada2 (#3298).

This is probably worth a unit test

Agreed, but the tricky part is that we don't have anything using meta attributes in core blocks. If we did, we'd have an obvious place to add a test simulating user input into meta, as a canary for all the moving parts of meta attributes. Obviously, we can just add a selector test for getPostMeta, but it wouldn't catch state schema changes.

but I have to go to WCUS right now.

As one does daily. 😁