(Closes #2499) scalarization transformation implementation

[LonelyCat124]

First implementation is here. I have unit tests for the private routines, I need to test it with code examples doing the full transformation properly but in theory its implemented here for now.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.86%. Comparing base (6f618c9) to head (ed75417). Report is 351 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2563   +/-   ##
=======================================
  Coverage   99.86%   99.86%           
=======================================
  Files         357      355    -2     
  Lines       48332    48402   +70     
=======================================
+ Hits        48266    48339   +73     
+ Misses         66       63    -3     

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[LonelyCat124]

@hiker Quick question on how the ordering of statements goes with the dependency system - if you have an assignment such as a = a + 1 does the a access on the RHS appear before the a on the LHS? I assume so (and that makes sense) but I just wanted to double check as I have a superfluous (and unreachable) if statement if so.

[LonelyCat124]

@sergisiso this is ready for a first look. I didn't add anything to user or dev guide for now, let me know if you think I should.

I'm waiting for hiker to clarify my question before I remove the code at lines 123 in the transformation, but I expect to remove those lines as I think they're unreachable.

[LonelyCat124]

@sergisiso I've addressed most of the comments here - I think the next_access one is a bigger issue than just here (and we need to decide if the variable access tooling should handle this or if we just do it in next_access, but I think we can do an implementation for this in the mean time anyway).

I need to still expand the tests for the apply routine and add documentation before another review though I think.

[sergisiso]

@LonelyCat124 I don't mind the order of these (if you put the associated TODOs), but wouldn't want to go very far with some logic that then will need to be deleted.