No PDB files installed on Windows

PDB files aren't installed when doing a Debug or RelWithDebInfo build on Windows.

This can be fixed by explicitly setting compiler generated PDB names:
```
if(WIN32)
set_target_properties(${libname} PROPERTIES
COMPILE_PDB_NAME "${libname}"
)
endif()
```

and installing both compiler and linker generated PDB files:
```
if(WIN32)
if(BUILD_SHARED_LIBS)
install(
FILES $
DESTINATION ${CMAKE_INSTALL_BINDIR}
OPTIONAL
)
else()
install(
FILES $/${libname}.pdb
DESTINATION ${CMAKE_INSTALL_LIBDIR}
OPTIONAL
)
endif()
endif()
```

for both Imath and PyImath libraries.

Inspect the CMake build and installation definitions for the Imath and PyImath libraries; the issue does not name specific files. Reproduce a Windows Debug or RelWithDebInfo build, then verify that both compiler- and linker-generated PDB files are installed for shared and static builds.

Written by the indexing model from the issue text.