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>

Cargo.lock

@@ -8374,6 +8374,7 @@ dependencies = [
  "revive-common",
  "revive-linker",
  "revive-runtime-api",
+ "revive-solc-json-interface",
  "revive-stdlib",
  "semver 1.0.25",
  "serde",
@@ -8406,6 +8407,18 @@ dependencies = [
  "revive-common",
 ]
 
+[[package]]
+name = "revive-solc-json-interface"
+version = "0.1.0-dev.12"
+dependencies = [
+ "anyhow",
+ "rayon",
+ "revive-common",
+ "semver 1.0.25",
+ "serde",
+ "serde_json",
+]
+
 [[package]]
 name = "revive-solidity"
 version = "0.1.0-dev.12"
@@ -8424,6 +8437,7 @@ dependencies = [
  "regex",
  "revive-common",
  "revive-llvm-context",
+ "revive-solc-json-interface",
  "semver 1.0.25",
  "serde",
  "serde_json",