feat(c-api) Implement wasm_func_type.

This patch creates a `wasm_functype_t::new` constructor, that is used
by the new `wasm_func_type` function, and the existing
`wasm_functype_new_inner` function.

lib/c-api/src/wasm_c_api/externals/function.rs

@@ -1,6 +1,6 @@
 use super::super::store::wasm_store_t;
 use super::super::trap::wasm_trap_t;
-use super::super::types::{wasm_functype_t, wasm_valkind_enum};
+use super::super::types::{wasm_functype_t, wasm_functype_t, wasm_valkind_enum};
 use super::super::value::{wasm_val_inner, wasm_val_t};
 use std::convert::TryInto;
 use std::ffi::c_void;
@@ -154,3 +154,8 @@ pub unsafe extern "C" fn wasm_func_param_arity(func: &wasm_func_t) -> usize {
 pub unsafe extern "C" fn wasm_func_result_arity(func: &wasm_func_t) -> usize {
     func.inner.ty().results().len()
 }
+
+#[no_mangle]
+pub extern "C" fn wasm_func_type(func: &wasm_func_t) -> Box<wasm_functype_t> {
+    Box::new(wasm_functype_t::new(func.inner.ty().clone()))
+}

lib/c-api/src/wasm_c_api/types/function.rs

@@ -17,6 +17,14 @@ impl wasm_functype_t {
             unreachable!("data corruption: `wasm_functype_t` does not contain a function")
         }
     }
+
+    pub(crate) fn new(function_type: FunctionType) -> Self {
+        Self {
+            extern_: wasm_externtype_t {
+                inner: ExternType::Function(function_type),
+            },
+        }
+    }
 }
 
 wasm_declare_vec!(functype);
@@ -52,10 +60,9 @@ unsafe fn wasm_functype_new_inner(
         .map(Into::into)
         .collect::<Vec<_>>();
 
-    let extern_ = wasm_externtype_t {
+    Some(Box::new(wasm_functype_t::new(FunctionType::new(
-        inner: ExternType::Function(FunctionType::new(params, results)),
+        params, results,
-    };
+    ))))
-    Some(Box::new(wasm_functype_t { extern_ }))
 }
 
 #[no_mangle]