Feature: ancestor face computation function for the scheme

[holke]

Closes #1738

Describe your changes here:

Add a new function to compute the face number of an ancestor face, given a lower level element and a subface.
Added a universal solution by iterating over the levels and the element_face_get_parent_face function.

Maybe we should extend testing, currently only the same and one level above is tested.

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[codecov]

Codecov Report

❌ Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.68%. Comparing base (1124119) to head (598a563).

Files with missing lines	Patch %	Lines
src/t8_schemes/t8_scheme_helpers.hxx	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1958      +/-   ##
==========================================
+ Coverage   75.66%   75.68%   +0.01%     
==========================================
  Files         105      105              
  Lines       18646    18669      +23     
==========================================
+ Hits        14109    14130      +21     
- Misses       4537     4539       +2     

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