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/standard_json/output/contract/evm/bytecode.rs

@@ -0,0 +1,34 @@
+//! The `solc --standard-json` output contract EVM bytecode.
+
+use serde::Deserialize;
+use serde::Serialize;
+
+/// The `solc --standard-json` output contract EVM bytecode.
+#[derive(Debug, Serialize, Deserialize, Clone)]
+#[serde(rename_all = "camelCase")]
+pub struct Bytecode {
+    /// The bytecode object.
+    pub object: String,
+}
+
+impl Bytecode {
+    /// A shortcut constructor.
+    pub fn new(object: String) -> Self {
+        Self { object }
+    }
+}
+
+/// The `solc --standard-json` output contract EVM deployed bytecode.
+#[derive(Debug, Serialize, Deserialize, Clone)]
+#[serde(rename_all = "camelCase")]
+pub struct DeployedBytecode {
+    /// The bytecode object.
+    pub object: String,
+}
+
+impl DeployedBytecode {
+    /// A shortcut constructor.
+    pub fn new(object: String) -> Self {
+        Self { object }
+    }
+}