Improvement: Element data for mesh handle is now defined via mesh competence

[lenaploetzke]

Closes #2185

Describe your changes here:
mesh handle: Having element data is now optional via a mesh competence. This makes it easier to define additional mesh competences, e.g. needed for #2115. Moreover, the code is cleaner as the element related functions are outsources in an other file. We do not need the requires clauses if the ElementData is void anymore.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.47%. Comparing base (eb1d4d2) to head (ee1f913).

Additional details and impacted files

@@                         Coverage Diff                          @@
##           handle_add-partition-and-balance    #2184      +/-   ##
====================================================================
+ Coverage                             78.46%   78.47%   +0.01%     
====================================================================
  Files                                   115      116       +1     
  Lines                                 19133    19144      +11     
====================================================================
+ Hits                                  15013    15024      +11     
  Misses                                 4120     4120              

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