Python API __repr__ printers for more objects

[disconnect3d]

It would be nice to have __repr__ in more (or all) Python classes, e.g., operand displays could have more useful repr than just:

<capstone.x86.X86Op object at 0x7fe856a06640>

We did sth similar recently for the CsInsn in #1625

A lot of classes inherit from ctypes.Structure like in https://github.com/aquynh/capstone/blob/1b5014515d0d671048e2b43ce483d38d85a2bc83/bindings/python/capstone/x86.py so this could probably be implemented somehow generally by adding a base class that would inherit from ctypes.Structure and would use, .e.g., a _format field if its defined in the inherited class to go over fields we want to show and display them with given format?

[disconnect3d]

This could also account for custom printing logic for a given field. For example enum fields could be displayed in their enum string instead of just bare integer value.