Add Rust API to grab the contents of a slint::Window into a slint::SharedImageBuffer #15546

Job	Run time
cpp_test_driver (ubuntu-22.04)	5m 28s
android	2m 2s
cpp_test_driver (macos-12)	4m 52s
build_and_test (ubuntu-22.04, stable)	2m 46s
cpp_cmake (ubuntu-22.04)	5m 17s
cpp_test_driver (windows-2022)	5m 6s
build_and_test (ubuntu-22.04, 1.73)	3m 4s
cpp_cmake (macos-12)	5m 19s
esp-idf-quick	5m 2s
build_and_test (macos-12, stable)	3m 10s
cpp_cmake (windows-2022)	5m 10s
build_and_test (windows-2022, stable)	2m 56s
ffi_32bit_build	1m 8s
build_and_test (windows-2022, 1.73)	2m 56s
fmt_test	1m 52s
build_and_test (windows-2022, beta, --exclude ffmpeg --exclude gstreamer-player)	3m 1s
mcu (pico-st7789, thumbv6m-none-eabi)	31s
mcu (stm32h735g, thumbv7em-none-eabihf)	42s
mcu_esp	2m 18s
node_test (ubuntu-22.04)	2m 6s
miri	42s
node_test (macos-12)	2m 42s
python_test (ubuntu-22.04)	1m 42s
node_test (windows-2022)	2m 1s
python_test (macos-12)	1m 33s
uefi-demo	36s
python_test (windows-2022)	2m 2s
updater_test (0.3.0)	1m 58s
docs / docs	2m 1s
tree-sitter / tree-sitter-tests	9s
wasm / wasm	1m 33s
wasm_demo / wasm_demo	1m 19s
cpp_package_test	1s
wasm / lint-slintpad	1s
wasm / build-slintpad	1s
	1h 23m 7s

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