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/solc-json-interface/src/warning.rs

@@ -0,0 +1,48 @@
+//! `resolc` custom compiler warnings.
+//!
+//! The revive compiler adds warnings only applicable when compilng
+//! to the revive stack on Polkadot to the output.
+
+use std::str::FromStr;
+
+use serde::Deserialize;
+use serde::Serialize;
+
+// The `resolc` custom compiler warning.
+#[derive(Debug, Serialize, Deserialize, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Warning {
+    EcRecover,
+    SendTransfer,
+    ExtCodeSize,
+    TxOrigin,
+    BlockTimestamp,
+    BlockNumber,
+    BlockHash,
+}
+
+impl Warning {
+    /// Converts string arguments into an array of warnings.
+    pub fn try_from_strings(strings: &[String]) -> Result<Vec<Self>, anyhow::Error> {
+        strings
+            .iter()
+            .map(|string| Self::from_str(string))
+            .collect()
+    }
+}
+
+impl FromStr for Warning {
+    type Err = anyhow::Error;
+
+    fn from_str(string: &str) -> Result<Self, Self::Err> {
+        match string {
+            "ecrecover" => Ok(Self::EcRecover),
+            "sendtransfer" => Ok(Self::SendTransfer),
+            "extcodesize" => Ok(Self::ExtCodeSize),
+            "txorigin" => Ok(Self::TxOrigin),
+            "blocktimestamp" => Ok(Self::BlockTimestamp),
+            "blocknumber" => Ok(Self::BlockNumber),
+            "blockhash" => Ok(Self::BlockHash),
+            _ => Err(anyhow::anyhow!("Invalid warning: {}", string)),
+        }
+    }
+}