Allowing pybullet to use filepath or string

[cadop]

Just an idea, if there is some suggested way to implement this I would be up for doing it.

Currently pybullet asks for a file to load a urdf/obj/etc. Which causes some workarounds like tempfiles that are not always convenient (e.g. #3850).

For some cases, like modifying/creating a mesh or robot in memory would be convenient to pass directly to bullet without it needing a file to reload the string. Another case is creating multiple instances of pybullet in parallel with slight modifications to a robot or obj file, which then relies on disk operations.

One idea I had was to make an optional parameter for an object string to pybullet (e.g. File=False). I haven't looked too much into this, but I guess there could be a ctypes conversion in pybullet.c and have the c++ side skip IO?