Pybind install
Update build/install logic for pybind11 modules so they can be used in CMB ModelBuilder.
- Relocate each pybind library (e.g., smtkPybindCommon.so on linux) to its respective python module (folder).
- Initialize SMTK_PYTHON_MODULEDIR for both shiboken and pybind11 builds (was shiboken only).
- Renames the pybind libraries to include an underscore prefix (e.g., _smtkPybindCommon.so) to indicate they are for internal use.
- Adds pybind11 wrappers for smtk::simulation module, which is needed for CMB export. This includes adding the obscure but much-needed ExportSpec::InternalConverterDoNotUse() method.
Tested these changes with CMB to confirm that we can run export scripts. (The scripts don't necessarily go to successful completion, but that's for a different MR to the simulation-workflows repo.)