Teach find_package to search CPS search paths, and to look for CPS file
names. Modify the set of file names to also include the file type (CPS
or CMake-script). Modify the search function to allow specifying which
file type(s) to consider.
During full path search, each possible path is searched for only one of
the two possible file types. However, subsequent runs, or when
considering a user-specified path (<name>_DIR), CMake will look for both
file types.
Note that this only adds the new path search logic as described above;
CMake does not yet know how to read CPS files, and there is a high
likelihood that Bad Things will happen if it tries. However, this seemed
like a good place to checkpoint.
b89e43b2bc