MVKShaderConverterTool add support to output SPIR-V as header (.h) files.
Add MVKShaderConverterTool Xcode target.
Add MVKShaderConverterTool Package Xcode scheme.
fetchDependencies builds MVKShaderConverterTool and runs
it on shader files in VulkanSamples API-Samples directory.
All external library header references consistently include framework references.
Cleanup references to external library headers that are no longer required.
Simplify and consolidate external library header paths in Xcode projects.
Add MVK_EXCLUDE_SPIRV_TOOLS build option to avoid use of SPIRV-Tools library.
Remove all other references to headers within SPIRV-Tools library.
Refactor build scripts.
Update paths to MoltenVKGLSLToSPIRVConverter framework in demos.
Fix rare build race condition on MoltenVKShaderConverter link to MoltenVK.
