Entity revisions data producer

[rthideaway]

Splitting up new data producers as agreed in #859
This PR introduces Entity revisions data producer

[codecov]

Codecov Report

Merging #909 into 8.x-4.x will decrease coverage by 2.98%.
The diff coverage is 0%.

@@              Coverage Diff              @@
##             8.x-4.x     #909      +/-   ##
=============================================
- Coverage      64.62%   61.63%   -2.99%     
- Complexity       624      678      +54     
=============================================
  Files             93       95       +2     
  Lines           1340     1405      +65     
=============================================
  Hits             866      866              
- Misses           474      539      +65

Impacted Files	Coverage Δ	Complexity Δ
...QL/DataProducer/Field/EntityReferenceRevisions.php	0% <0%> (ø)	40 <40> (?)
src/GraphQL/Buffers/EntityRevisionBuffer.php	0% <0%> (ø)	14 <14> (?)

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[rthideaway]

Adjusted access. Should be ready for re-review

[rthideaway]

We have this problem on some other places in the code base (translations loaded after access check). If this gets approved and merged, will fix it also there.

[fubhy]

We have this problem on some other places in the code base (translations loaded after access check). If this gets approved and merged, will fix it also there.

Yes please. That would be great.