Add `headless` argument to `lvk::initWindow()` #1475

Job	Run time
Android (Ubuntu)	6m 44s
cmake-test-ubuntu (Ubuntu - Clang, ubuntu-latest, Debug, clang-16, clang++-16, Unix Makefiles)	3m 51s
cmake-build-macos (macOS - Clang (Xcode), macos-latest, Debug, clang, clang++, Xcode, -DLVK_WITH_...	3m 48s
cmake-build (Ubuntu - Clang, ubuntu-latest, Debug, clang-16, clang++-16, Unix Makefiles)	3m 46s
cmake-build (Windows - MSVC 2022 (glslang), windows-latest, Debug, cl, cl, Visual Studio 17 2022,...	4m 13s
cmake-build (Ubuntu - Clang (Wayland), ubuntu-latest, Debug, clang-16, clang++-16, Unix Makefiles...	3m 42s
	26m 4s

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