factor out solc JSON interface crate (#264)

The differential testing framework will make a second consumer. There
seems to be no re-usable Rust crate for this. But we already have
everything here, just needs a small refactor to make it fully re-usable.

- Mostly decouple the solc JSON-input-output interface types from the
`solidity` frontend crate
- Expose the JSON-input-output interface types in a dedicated crate

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/llvm-context/Cargo.toml

@@ -29,3 +29,4 @@ revive-common = { workspace = true }
 revive-runtime-api = { workspace = true }
 revive-linker = { workspace = true }
 revive-stdlib = { workspace = true }
+revive-solc-json-interface = { workspace = true }