android: add script in Android archive to create a SDK

Also,
- Move mingw's pkg-support into build-scripts
- Add type annotations to python scripts for mypy
- ci: use v4 tag of actions/cache
- cmake: use PYTHON3_EXECUTABLE for running xxd.py
  (Python3::Interpreter is not always recognized.)

CMakeLists.txt

@@ -3583,8 +3583,11 @@ if(NOT SDL_DISABLE_INSTALL)
   if(ANDROID)
     if(TARGET SDL3-jar)
       set(SDL_INSTALL_JAVADIR "${CMAKE_INSTALL_DATAROOTDIR}/java" CACHE PATH "Path where to install java clases + java sources")
+      set(PROGUARD_RULES_PATH "${CMAKE_CURRENT_SOURCE_DIR}/android-project/app/proguard-rules.pro")
       install(FILES $<TARGET_PROPERTY:SDL3-jar,INSTALL_FILES>
         DESTINATION "${SDL_INSTALL_JAVADIR}/SDL3")
+      install(FILES "${PROGUARD_RULES_PATH}" RENAME "proguard.txt"
+        DESTINATION "${SDL_INSTALL_JAVADIR}/SDL3")
       configure_package_config_file(cmake/SDL3jarTargets.cmake.in SDL3jarTargets.cmake
         INSTALL_DESTINATION "${SDL_SDL_INSTALL_CMAKEDIR}"
         PATH_VARS SDL_INSTALL_JAVADIR