Revise vtk2trixi so that it returns a NamedTuple instead of an InitialCondition

[marcelschurer]

This PR changes the return type of the vtk2trixi function from InitialCondition to a NamedTuple and adds several other important quantities.

[svchb]

@LasNikas Didn't you have code somewhere to do a restart via vtk2trixi? If yes it still needs to be updated.

[LasNikas]

@LasNikas Didn't you have code somewhere to do a restart via vtk2trixi? If yes it still needs to be updated.

@svchb No, but it is still a breaking change because the return type has changed.

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.59%. Comparing base (32679eb) to head (0b22696).

Files with missing lines	Patch %	Lines
test/io/read_vtk.jl	90.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #959      +/-   ##
==========================================
- Coverage   89.60%   89.59%   -0.01%     
==========================================
  Files         120      120              
  Lines        8588     8634      +46     
==========================================
+ Hits         7695     7736      +41     
- Misses        893      898       +5     

Flag	Coverage Δ
total	89.59% <92.00%> (-0.01%)	⬇️
unit	65.30% <92.00%> (+0.46%)	⬆️

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