Update proto to readonly array reference (fix downstream issue)

Author: wwwillchen

mesop/web/src/dev_tools/editor_panel/editor_fields/editor_fields.ts

@@ -50,7 +50,7 @@ type Prefixes = Prefix[];
 })
 export class EditorFields {
   @Input()
-  fields!: EditorField[];
+  fields!: readonly EditorField[];
 
   @Input()
   prefixes: Prefixes = [];
@@ -255,7 +255,7 @@ export class EditorFields {
     return display;
   }
 
-  getFieldsForListField(field: EditorField): EditorField[] {
+  getFieldsForListField(field: EditorField): readonly EditorField[] {
     return (
       field
         .getType()!

mesop/web/src/dev_tools/editor_panel/editor_panel.ts

@@ -120,7 +120,7 @@ export class EditorPanel {
     );
   }
 
-  getFields(): EditorField[] {
+  getFields(): readonly EditorField[] {
     return this.getComponentConfig()?.getFieldsList() ?? [];
   }