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/optimizer/settings/mod.rs

@@ -2,6 +2,7 @@
 
 pub mod size_level;
 
+use revive_solc_json_interface::SolcStandardJsonInputSettingsOptimizer;
 use serde::Deserialize;
 use serde::Serialize;
 
@@ -226,3 +227,18 @@ impl std::fmt::Display for Settings {
         )
     }
 }
+
+impl TryFrom<&SolcStandardJsonInputSettingsOptimizer> for Settings {
+    type Error = anyhow::Error;
+
+    fn try_from(value: &SolcStandardJsonInputSettingsOptimizer) -> Result<Self, Self::Error> {
+        let mut result = match value.mode {
+            Some(mode) => Self::try_from_cli(mode)?,
+            None => Self::cycles(),
+        };
+        if value.fallback_to_optimizing_for_size.unwrap_or_default() {
+            result.enable_fallback_to_size();
+        }
+        Ok(result)
+    }
+}