(Closes #2854) exclude char assignments from ACC KERNELS regions

[arporter]

Small PR that picks up the functionality already in ArrayAssignment2LoopsTrans and copies it into ACCKernelsTrans.

[arporter]

I'm not entirely happy with the code duplication here but this PR is for OpenACC functionality and the existing check is in the conversion of array assignments to loops so there's not much common ground between them.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.88%. Comparing base (2307ac7) to head (4c65986).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2857   +/-   ##
=======================================
  Coverage   99.88%   99.88%           
=======================================
  Files         359      359           
  Lines       50833    50847   +14     
=======================================
+ Hits        50777    50791   +14     
  Misses         56       56           

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[arporter]

I've solved the duplication by making the validation a separate classmethod in ArrayAssignment2LoopsTrans. Coverage is 100%. I'll set the integration tests running.

[arporter]

Integration test for NEMOv4 failed but only because of a small bug where we failed to lower-case the name of a structure component when getting its datatype. I'll re-run that job.

[arporter]

Integration tests now green. Ready for review from anyone :-)

[arporter]

I changed my mind - it turns out my 'fix' revealed general case-sensitivity problems in our storage of components of a StructureType. I've fixed these now and extended the tests slightly.