Generalize function for AnalysisSurfaceIntegral

[andrewwinters5000]

This adds the x coordinate and the time t as input arguments for the variable function that can be integrated along a physical boundary via AnalysisSurfaceIntegral. This will allow the callback to compute integrated quantities on boundaries that depend on the solution u as well as boundary data that may be space and/or time dependent. Currently, the variable function can only use the solution u to compute boundary quantities.

[github-actions]

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[DanielDoehring]

LGTM!

This makes the computation of the existing integrals slightly more expensive as now also the node coordinates are computed, but that is hopefully not too dramatic.

Thanks Andrew for the additional comments, it is always helpful to have a second person expressing their understanding!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.30%. Comparing base (c6fc9c5) to head (d06320e).
Report is 1 commits behind head on main.

Additional details and impacted files

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##             main    #1902   +/-   ##
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  Coverage   96.30%   96.30%           
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  Files         448      448           
  Lines       36079    36081    +2     
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+ Hits        34745    34747    +2     
  Misses       1334     1334           

Flag	Coverage Δ
unittests	96.30% <100.00%> (+<0.01%)	⬆️

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[andrewwinters5000]

Thanks Andrew for the additional comments, it is always helpful to have a second person expressing their understanding!

No problem! It is easy to lose track of the normal scaling and what is meant between normal_direction and a normal_vector. So, these extra comments hopefully avoid headaches in the future.