Bulk lazy initialization of FunctionDefinitions (#1425)

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>
Co-authored-by: Edoardo Vacchi <evacchi@users.noreply.github.com>

internal/wasm/module_instance.go

@@ -203,7 +203,7 @@ func (m *ModuleInstance) ExportedFunctionDefinitions() map[string]api.FunctionDe
 	result := map[string]api.FunctionDefinition{}
 	for name, exp := range m.Exports {
 		if exp.Type == ExternTypeFunc {
-			result[name] = &m.Definitions[exp.Index]
+			result[name] = m.Source.FunctionDefinition(exp.Index)
 		}
 	}
 	return result