CMake: Add CMakeUserPresets.json

CMake 3.19 added CMakePresets.json, which is intended to be
version-controlled, and CMakeUserPresets.json, which should NOT
be version-controlled. Add CMakeUserPresets.json to the gitignore.

https://cmake.org/cmake/help/latest/manual/cmake-presets.7.html

CMake.gitignore

@@ -9,3 +9,4 @@ install_manifest.txt
 compile_commands.json
 CTestTestfile.cmake
 _deps
+CMakeUserPresets.json