feat(goctl): Add api parser (#2585)

tools/goctl/api/spec/spec.go

@@ -21,9 +21,9 @@ type (
 
 	// ApiSpec describes an api file
 	ApiSpec struct {
-		Info    Info
-		Syntax  ApiSyntax
-		Imports []Import
+		Info    Info      // Deprecated: useless expression
+		Syntax  ApiSyntax // Deprecated: useless expression
+		Imports []Import  // Deprecated: useless expression
 		Types   []Type
 		Service Service
 	}
@@ -70,6 +70,7 @@ type (
 
 	// Route describes api route
 	Route struct {
+		// Deprecated: Use Service AtServer instead.
 		AtServerAnnotation Annotation
 		Method             string
 		Path               string