Add array::View interoperability with mdspan

[wdeconinck]

With this PR, following API is added to array::View:

• array::View view{mdspan} constructor
• auto mdspan = view.as_mdspan() function to create an mdspan.

Due to general assumptions of array::View, the as_mdspan() function creates a mdspan with layout_stride and fully dynamic extents:

mdspan<T, dextents<size_t,rank>, layout_stride, default_accessor<T>>

The array::IndexView follows a similar API, but the as_mdspan() function creates a mdspan with index_accessor, to convert contain values (indices) to base 1 when Fortran is used.

mdspan<T, dextents<size_t,rank>, layout_stride, index_accessor<T,ATLAS_HAVE_FORTRAN>>

💣💥☠️ Static Analyzer Report ☠️💥💣
https://sites.ecmwf.int/docs/atlas/static-analyzer/PR-304

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.19588% with 26 lines in your changes missing coverage. Please review.

Project coverage is 79.58%. Comparing base (cdbb4dc) to head (1ad3b48).
Report is 6 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/atlas/array/native/NativeArrayView.h	0.00%	12 Missing ⚠️
src/atlas/array/native/NativeIndexView.h	25.00%	12 Missing ⚠️
src/atlas/array/LocalView.h	88.88%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #304      +/-   ##
===========================================
+ Coverage    79.11%   79.58%   +0.46%     
===========================================
  Files          895      895              
  Lines        59956    68911    +8955     
===========================================
+ Hits         47435    54842    +7407     
- Misses       12521    14069    +1548     

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