Extract: Improved region-outlining for complex procedures

[mlange05]

This change brings various improvements to enable the use of outine_pragma_regions for more complex code regions. This is intended to eventually allow us to combine pragma-based extraction with auto-parallelisation to re-rewrite complex control-flow sections.

In particular, this PR refactors the utility structure to allow invocations per-region, deals with derived type symbols and arguments, and imposes an ordering on extracted argument signatures. There are also other small improvements added, as well as a utility to remove unused imports and import symbols.

In more detail:

• Use of Transformer, instead of the more complex NestedMaskedTransformer to replace PragmaRegion nodes
• Separation of the outer loop over subroutines from the specific single call-subroutine extraction for a single region
• A new utility to remove unused imports and trim unused symbols from import statements within a routine
• Ability to handle C-style imports when pragma-outlining sburoutines
• Resolving explicitly requested argument symbols (via the "intent" notation) from the parent routine. This allows explicitly requesting arguments that might not be used in the body, but are necessary for shape info in the spec of the extracted routine.
• Handling of derived-type symbols in extracted body/routine, in particular ensuring that only the parent is added to the extracted routine signature
• Additional tests for derived-type arguments and associated symbols in extracted bodies/routines. The latter is not strictly needed, but useful to have.
• Explicit ordering of arguments for reproducibility - this will use lexicographic base ordering, but put derived-type arguments, before array arguments, before scalar arguments.

[github-actions]

Documentation for this branch can be viewed at https://sites.ecmwf.int/docs/loki/412/index.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.07%. Comparing base (58adb24) to head (657550c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #412      +/-   ##
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+ Coverage   93.05%   93.07%   +0.02%     
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  Files         198      198              
  Lines       39320    39464     +144     
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+ Hits        36588    36732     +144     
  Misses       2732     2732              

Flag	Coverage Δ
lint_rules	96.39% <ø> (ø)
loki	93.02% <100.00%> (+0.02%)	⬆️

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