TmpFile constructs a temporary file that can be written to, and is automatically deleted on destruction.
Will be used to create a temporary source file for verifying generated HLSL and MSL against their shader compilers.
Change-Id: Ieaa6f257b93f4f2193dafe6297603816f6964928
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/41941
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>