CMake modernization #1128

Job	Run time
Emscripten	1m 16s
Linux (clang, clang++, -DRMLUI_ENABLE_PRECOMPILED_HEADERS=OFF -DRMLUI_SAMPLES_BACKEND=GLFW_GL2)	2m 19s
Linux (clang, clang++, -DRMLUI_SAMPLES_BACKEND=SDL_VK -DSDL_LIBRARY=SDL2 -DSDL_INCLUDE_DIR=/usr/i...	2m 16s
Linux (-DRMLUI_BUILD_TESTING=ON -DRMLUI_ENABLE_PRECOMPILED_HEADERS=OFF, true)	1m 57s
Linux (-DRMLUI_ENABLE_LOTTIE_PLUGIN=ON -DRMLUI_SAMPLES_BACKEND=X11_GL2)	2m 41s
Linux (-DRMLUI_DISABLE_RTTI_AND_EXCEPTIONS=ON -DRMLUI_SAMPLES_BACKEND=SDL_GL2 -DSDL_LIBRARY=SDL2 ...	2m 20s
Linux (-DRMLUI_NO_THIRDPARTY_CONTAINERS=ON -DRMLUI_SAMPLES_BACKEND=SFML_GL2)	2m 24s
Linux (-DRMLUI_SAMPLES_BACKEND=SDL_VK -DRMLUI_VK_DEBUG=ON -DRMLUI_ENABLE_PRECOMPILED_HEADERS=OFF ...	1m 47s
macOS (-DRMLUI_SAMPLES_BACKEND=GLFW_GL2)	6m 4s
Windows (-DRMLUI_SAMPLES_BACKEND=Win32_VK -DRMLUI_VK_DEBUG=ON)	50s
Windows (-DRMLUI_SAMPLES_BACKEND=SDL_VK -DRMLUI_BUILD_LUA_BINDINGS_FOR_LUAJIT=ON)	1m 3s
	24m 57s

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