(towards #2577) Add support for pointer assignments

[sergisiso]

[codecov[bot]]

Codecov Report

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

Project coverage is 99.85%. Comparing base (4d10caa) to head (09d4cec).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2583      +/-   ##
==========================================
- Coverage   99.86%   99.85%   -0.01%     
==========================================
  Files         351      352       +1     
  Lines       48396    48455      +59     
==========================================
+ Hits        48331    48386      +55     
- Misses         65       69       +4     

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[sergisiso]

This is ready for a first look from @arporter or @hiker . It adds support for pointer assignments (removes the CodeBlocks), but not symbol attributes (does not remove UnknownFortranType for its symbols). It also adds support in the frontend for Fortran2003.Data_Pointer_Object fparser object. For now I added some broad protections in the base loop_trans and region_trans to prevent transformation to apply to code that have pointer assignments (which can be disabled with a transformation option).

[sergisiso]

@arporter This is ready for next review. In comparison to the first review I found out that pointer expressions that have array accessor ranges in the inner element are not described like regular arrays in the standard/fparser. So I decided to not support these cases yet - they are CodeBlocks as before.

[sergisiso]

@arporter This is ready for another review