Refactor finding python

Use `find_package(Python ..)` if available, instead of the deprecated
`find_package(PythonInterp)` CMake module.

googletest/cmake/internal_utils.cmake

@@ -244,7 +244,13 @@ function(cxx_executable name dir libs)
 endfunction()
 
 # Sets PYTHONINTERP_FOUND and PYTHON_EXECUTABLE.
-find_package(PythonInterp)
+if ("${CMAKE_VERSION}" VERSION_LESS "3.12.0")
+  find_package(PythonInterp)
+else()
+  find_package(Python COMPONENTS Interpreter)
+  set(PYTHONINTERP_FOUND ${Python_Interpreter_FOUND})
+  set(PYTHON_EXECUTABLE ${Python_EXECUTABLE})
+endif()
 
 # cxx_test_with_flags(name cxx_flags libs srcs...)
 #