`wasm-encoder` relocation data generation

[daxpedda]

This is a feature request to add an equivalent for wat2wasm --relocatable to wasm-tools for feature parity.

I'm still stuck with wabt to be able to generate Wasm object files from WAT to link against.

[alexcrichton]

You might be interested in WebAssembly/tool-conventions#258 which has some related discussion to this. Otherwise though personally I'm not familiar enough with --relocatable to say much about it. My impression is that this would ideally be a text-format-based annotation to avoid the need to add flags to the text->binary transform (which ideally is a function without parameters other than the text IMO).

[daxpedda]

@Spxg has written an implementation for our use-case: rwat. It turns out that doing this externally with wasm-tools libraries is quite the messy workaround.

Our next step would be to implement the complete proposed spec and I would really prefer a cleaner implementation. Would wasm-tools be up for an experimental implementation? E.g. like Wasm proposals that have no yet reached stage 4?