[Idea] Relative position/state sensor

[Ivan-267]

Note: The exact features of the sensor and whether to implement it is yet to be determined, it's just an idea at this point.

The most basic functionality would include adding a relative position vector from an object to an object that is clipped at some distance and normalized.

Some possible additions to the basic idea (not all would necessarily be added):

• Allowing multiple objects (an array of Node2D/3D) could be useful, and/or all objects that have a tag.
• Including additional object properties such as linear velocity for objects that have it.
• Similar to above, including custom properties that the user specifies.

The name for the state sensor is inspired by https://huggingface.co/docs/simulate/main/api/sensors#simulate.StateSensor, although I'm not familiar with the exact features or implementation of the sensor in Simulate.