Implement static data slicing

[sffc]

I have been talking about data slicing via static code analysis for a long time. I did early experiments to demonstrate that this is possible. This issue is to track the eventual implementation of this feature.

How it will work:

1. Dead code elimination produces an optimized binary
2. We inspect the optimized binary to find all ResourceKeys
3. We build a new data bundle with only the matched keys

Step 2 is the tricky part. Some experimentation will be necessary. The solution which I know will work would be to conditionally annotate the data model of ResourceKey with a special value that can be found via strings(1) or a similar tool.

[iainireland]

Is the expectation that users will build an optimized binary, inspect it offline, and emit a key file to feed into datagen, then check in the results of datagen? Or that this will be integrated into the build process in CI?

[sffc]

Eventually I would like the tooling to be fairly transparent to clients. At first though it would probably be several manual steps in sequence.