Build IDs to match DWARF debug files #1306

Now that DWARF debug information are becoming a thing I was looking into what is necessary to provide breakpad style deferred symbolication. The initial blocker that came up was that there is no good way to match up the main wasm file and the companion wasm file containing debug info.

The way this works best normally is with GUIDs that identify the pairing. In mach we have UUIDs, in ELF the GNU build ID and on Windows the PDB signature and age.

Ideally we would have a UUID stored in WASM files as well. This would permit services like Sentry or Symbolicator be able to fetch debug information files from external sources by knowledge of the UUID alone.