[Cmake] Don't blindly overwrite CMAKE_MODULE_PATH.

[marsupial]

Description of Change(s)

Make sure CMAKE_MODULE_PATH passed via command line has precedence over USD.

Fixes Issue(s)

If there are non standard paths/ installs CMAKE_MODULE_PATH is a much easier route than specifying multiple locations, but USD is currently overwriting any CMAKE_MODULE_PATH passed to it.

[meshula]

I think, but am not positive, that CMake searches first to last? If that is true, wouldn't you want the existing CMAKE_MODULE_PATH to have the lowest precedence?

The documentation is ... lacking. https://cmake.org/cmake/help/latest/variable/CMAKE_MODULE_PATH.html

If this change were to be made, it would probably also be preferable that the cmake scripts in USD be prefixed with USD, e.g. USD_Public.cmake, USD_Packages.cmake, etc., as there is a greater than zero probability that if you allow external to USD CMAKE_MODULE_PATHS, conflicting files may appear in the total search path.

[marsupial]

If you don't use -DCMAKE_MODULE_PATH=, then CMAKE_MODULE_PATH is empty.
So like $PATH, you're trying to override behavior in favor of something custom/better.

[jtran56]

Filed as internal issue #USD-4737.