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/src/polkavm/metadata_hash.rs

@@ -1,29 +0,0 @@
-//! The metadata hash mode.
-
-use std::str::FromStr;
-
-use serde::Deserialize;
-use serde::Serialize;
-
-/// The metadata hash mode.
-#[derive(Debug, Serialize, Deserialize, Clone, Copy, PartialEq, Eq, Hash)]
-pub enum MetadataHash {
-    /// Do not include bytecode hash.
-    #[serde(rename = "none")]
-    None,
-    /// The default keccak256 hash.
-    #[serde(rename = "keccak256")]
-    Keccak256,
-}
-
-impl FromStr for MetadataHash {
-    type Err = anyhow::Error;
-
-    fn from_str(string: &str) -> Result<Self, Self::Err> {
-        match string {
-            "none" => Ok(Self::None),
-            "keccak256" => Ok(Self::Keccak256),
-            _ => anyhow::bail!("Unknown bytecode hash mode: `{}`", string),
-        }
-    }
-}

crates/llvm-context/src/polkavm/mod.rs

@@ -3,7 +3,6 @@
 pub mod r#const;
 pub mod context;
 pub mod evm;
-pub mod metadata_hash;
 
 pub use self::r#const::*;