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

[lenaploetzke]

Describe your changes here:
Closes #2185. Update of #2184 because something got messed up in git.

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[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.57%. Comparing base (101b546) to head (b46f417).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
mesh_handle/data_handler.hxx	96.42%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2242      +/-   ##
==========================================
- Coverage   82.59%   82.57%   -0.02%     
==========================================
  Files         115      116       +1     
  Lines       18548    18556       +8     
==========================================
+ Hits        15320    15323       +3     
- Misses       3228     3233       +5     

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[Davknapp]

A first round of comments.

[Davknapp]

I think we don't need to reserve the memory for the vector. std::move should only swap pointers here, so we don't need to allocate new memory. However you should mention in the comment, that element_data is moved, not copied.

[lenaploetzke]

I thought i needed the reserve to avoid a reallocation if we later exchange ghost data (therefore i reserve more space then needed for element_data). What do you think?

[Davknapp]

The move command often works by swapping the internal pointers. Therefore it is counterintuitive to reserve memory before swapping the pointers.
Maybe the name of the function should indicate too, that you are using a move assignement here.

if you want to ensure that you have more space than you currently have you should move and then reserve.

[lenaploetzke]

Yeah i think i got it now. I did not rename the function but wrote an additional note in the documentation