Fields are not reset during MappingInfo().reinit_*()

[jh66637]

@bergbauer

During adding the test in #15292 I found that some fields are not cleared before they are filled again in reinint_*(). Therefore, having a sequence of reinits leads to unwanted behavior.

In my case, I called reinit_faces() and reinit_cells() on the same MappingInfo object and got the wrong JxW due to a mismatch of quadrature indices. Using a new object works. In this particular case, e.g., n_q_points_unvectorized is not cleared in reinit_cells(). I can fix that, but I am not as familiar with all the code and will probably forget some fields which should be cleared. Would you mind taking a look?

[bergbauer]

I will have a look!