Investigate find_program()

[memsharded]

At the moment find_program() paths are defined in conan_toolchain.cmake, so they will not work with cmake-conan integration.

They are intended for tool_requires, but also if tool_requires do not have find_package() in many cases, what would be the possibilities?

We could parse the output json and inject the respective paths in CMAKE_PROGRAM_PATHS, like conan_toolchain.cmake does, but someone should call conan install in the first place, and I am not sure we can rely on a random find_package() of another dependency for this.

cc/ @rollebolle

[jcar87]

#626