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.)

test/CMakeLists.txt

@@ -334,7 +334,7 @@ function(files2headers OUTPUT)
             # Don't add the 'output' header to the output, to avoid marking them as GENERATED
             # (generated files are removed when running the CLEAN target)
             add_custom_command(OUTPUT "${intermediate}"
-                COMMAND Python3::Interpreter "${xxd}" -i "${CMAKE_CURRENT_SOURCE_DIR}/${input}" "-o" "${intermediate}"
+                COMMAND "${Python3_EXECUTABLE}" "${xxd}" -i "${CMAKE_CURRENT_SOURCE_DIR}/${input}" "-o" "${intermediate}"
                 COMMAND "${CMAKE_COMMAND}" -E copy_if_different "${intermediate}" "${output}"
                 DEPENDS "${xxd}" "${bmp}"
             )