wasm_interp: simplified ImportDispatcher

We don't really need a trait for the 'import module' concept.

crates/wasm_interp/src/lib.rs

@@ -2,9 +2,25 @@ mod call_stack;
 mod instance;
 pub mod test_utils;
 mod value_stack;
-mod wasi;
+pub mod wasi;
+
+// Main external interface
+pub use instance::Instance;
 
 // Exposed for testing only. Should eventually become private.
 pub use call_stack::CallStack;
-pub use instance::{Action, Instance};
+pub use instance::Action;
 pub use value_stack::ValueStack;
+
+use roc_wasm_module::Value;
+
+pub trait ImportDispatcher {
+    /// Dispatch a call from WebAssembly to your own code, based on module and function name.
+    fn dispatch(
+        &mut self,
+        module_name: &str,
+        function_name: &str,
+        arguments: &[Value],
+        memory: &mut [u8],
+    ) -> Option<Value>;
+}