(closes #2642) Support structure type extends and contains

[sergisiso]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (72527a7) to head (83e6657).

Additional details and impacted files

@@            Coverage Diff             @@
##            master     #3563    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          397       397            
  Lines        55775     56023   +248     
==========================================
+ Hits         55775     56023   +248     

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[sergisiso]

@arporter @LonelyCat124 This is ready to review, it is a necesarry step to read the metadata using psyir. Wihtout this the embedded metadata ends up in an UnsupportedFortranType, and we still would need to parse it as a string.

It seems that Rupert started this path of parsing the metadata from the UnsupportedType as a string, at the moment I convert the new datatype back to an string and then pass it to existing metadata parsing to keep coverage of the existing tests (which feels odd). The previous PR adding this this feature #2644 also hit the same problem.

However, I have a follow up PR that converts the metadata parsing to take proper PSyIR (removing the need of fparser1 and string metadata parsing) and the code that lose coverage can be removed altoghether. But the resulting PR was huge. In fact I cut this branch to make the whole review more manegable.