[FEAT] Easier way to alter function signatures for `PYBIND11_OVERRIDE*`?

[EricCousineau-TRI]

Motivated by post here:
#2812 (comment)

One minor pain point I've ran into is wrapping calls to PYBIND11_OVERRIDE* macros.

We've worked around in Drake, but it ain't pretty. Example (older fork of pybind11, so you'll need to munge the names):
https://github.com/RobotLocomotion/drake/blob/6ee5e9325821277a62bd5cd5456ccf02ca25dab7/bindings/pydrake/systems/framework_py_systems.cc#L110-L159

As mentioned in the code, part of the reason for this was #1241 (return values, const lvalues, etc.).

\cc @YannickJadoul

[YannickJadoul]

Aren't such more complicate use cases why there is a (public) pybind11::get_override?

I agree the PYBIND11_OVERRIDE* macros are (very) limited, but the problem is adding extra macros might be horrible, if we don't wish to combinatorially explode the number of macros? :-(

Just thinking out loud: one option would be to add an example to the docs on how to use py::get_override. But I'm open/curious if you have something specific in mind, perhaps?

[EricCousineau-TRI]

\cc @rwgk @rhaschke for #2916