Metal: Refactor textureProj(Grad|Lod)[Offset] wrappers * Removed variadic macros. * Updated emitter to not output unused variants. * Added MSL compile guards to not fail shader compilation on macOS 10.15. Bug: angleproject:368059227 Change-Id: If9d9479c056da6a76cff78c7c5b42101a0fcce1e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5893255 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>