Add helper function to generate a debug symbol wheel

[AlexyPellegrini]

This is currently not even done in VTK, but should be doable.

The goal is to build the wheels in pseudo-RelWithDebInfo mode (in practice, Release with custom options), with the following do be done:

• On Linux, use the -gsplit-dwarf (https://gcc.gnu.org/wiki/DebugFission)
• On Mac, this should already be the default, search for dSYM files for more information
• On Windows, PDB are already split

Then only package the debug information files into a dedicated wheel that can be installed by users to debug the released wheel.