Functionality of displacement sensor should go to some other class

[srosenbu]

Currently, the displacement sensor
https://github.com/BAMresearch/FenicsXConcrete/blob/main/src/fenicsxconcrete/sensor_definition/displacement_sensor.py
contains code that can evaluate a dolfinx.fem.Function object at any point. This functionality is needed in basically most sensors that access a Function, therefore I would put it into some other class, like PointSensor to avoid duplicate code

[srosenbu]

Also, computing the colliding cells is done in each call of measure. I don't know how fast this method is, but to me it seems like something that should belong in the __init__