MoltenVK: Use an external project instead of a pre-compiled dylib

Also, update MoltenVK to match Vulkan SDK 1.2.189.

Externals/MoltenVK/CMakeLists.txt

@@ -0,0 +1,18 @@
+include(ExternalProject)
+
+ExternalProject_Add(MoltenVK
+  GIT_REPOSITORY https://github.com/KhronosGroup/MoltenVK.git
+  GIT_TAG v1.1.5
+
+  CONFIGURE_COMMAND <SOURCE_DIR>/fetchDependencies --macos
+
+  BUILD_COMMAND make -C <SOURCE_DIR> macos
+  BUILD_IN_SOURCE ON
+  BUILD_BYPRODUCTS <SOURCE_DIR>/Package/Release/MoltenVK/dylib/macOS/libMoltenVK.dylib
+
+  INSTALL_COMMAND ""
+
+  LOG_CONFIGURE ON
+  LOG_BUILD ON
+  LOG_OUTPUT_ON_FAILURE ON
+)

Externals/MoltenVK/version.txt

@@ -1 +0,0 @@
-MoltenVK from https://vulkan.lunarg.com/sdk/home#mac, version 1.2.170.0