Declare _formatDescriptions[] in mvk_datatypes.mm as officially writable
because Clang now locates static const in non-writable memory.
Update build settings to Xcode 11.
Update MoltenVK_Runtime_UserGuide.md about embedding `libMoltenVK.dylib` in an application.
Add ExternalDependencies (Debug) scheme to ExternalDependencies Xcode project.
Add --debug option to fetchDependencies script.
Support Release, Debug & Latest directories in External/build directory.
Enable DEPLOYMENT_POSTPROCESSING build setting when compiling
SPIRV-Tools to avoid warning spam when building dylibs.
Disable visibility warnings when building MoltenVKShaderConverter
in Release mode from external libraries built in Debug mode.
Always use -Xlinker -w option when creating dylibs to disable visibility warnings.