Combine MoltenVKSPIRVToMSLConverter and MoltenVKGLSLToSPIRVConverter
frameworks into a single MoltenVKShaderConverter framework.
Update corresponding directory structures, symlinks, scripts, and build paths.
Update MoltenVK code to use new framework name for headers.
Add symlinks in API-Samples demo to support legacy
MoltenVKGLSLToSPIRVConverter header paths.
In addition to simplifying shader converter code and build management, the
use of only one shader converter framework fixes a race condition within Xcode,
prior to Xcode 12, when multiple targets use the same dependency XCFramework.
Refactor build scripts.
Update paths to MoltenVKGLSLToSPIRVConverter framework in demos.
Fix rare build race condition on MoltenVKShaderConverter link to MoltenVK.
