conanfile.py: Accept QTDIR in addition to QT_PATH

    def _get_cmake_prefix_path(self):
        # 'QT_PATH' provided as env variable in profile file which is part of the Qt essential binary
        # package(s). Installed under .conan/profiles
        cmake_prefix_path = os.environ.get("QT_PATH")
        if not cmake_prefix_path:
            raise QtConanError("'QT_PATH' not defined! The 'QT_PATH' needs to point to Qt installation directory.")
        print(f"CMAKE_PREFIX_PATH for '{self.name}/{self.version}' build is: {cmake_prefix_path}"