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.

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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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[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.