Port over loop handling utils from PSyACC

[joewallwork]

Partially addresses #2717.

This PR merges functions from the loop module of PSyACC into PSyclone.

[sergisiso]

@jwallwork23 Isn't this equivalent to the Loop.independent_iterations method? (I think we considered this name for that method but decided the independent iterations could be more generic)

[joewallwork]

@jwallwork23 Isn't this equivalent to the Loop.independent_iterations method? (I think we considered this name for that method but decided the independent iterations could be more generic)

Oh good, if there is already an equivalent method then that's one less thing to merge in :) Thanks!

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 99.86%. Comparing base (8367de1) to head (32dba72). Report is 475 commits behind head on master.

Files with missing lines	Patch %	Lines
src/psyclone/psyir/nodes/loop.py	96.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2754      +/-   ##
==========================================
- Coverage   99.86%   99.86%   -0.01%     
==========================================
  Files         354      354              
  Lines       49010    49041      +31     
==========================================
+ Hits        48946    48976      +30     
- Misses         64       65       +1     

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[joewallwork]

Thanks again for your review on this @arporter. I haven't fully tested the new functionality of ParallelLoopTrans but I think enough of this PR is invalid that I'll close it and consider opening a new one if it any of it turns out to be important.