feat: add InputObjectDefinition::is_one_of (#1176)

Author: obmarg

cynic-parser/src/type_system/extensions.rs

@@ -1,6 +1,6 @@
 use std::{borrow::Cow, fmt};
 
-use crate::common::OperationType;
+use crate::{common::OperationType, type_system::InputObjectDefinition};
 
 use super::{Argument, Description, Directive, RootOperationTypeDefinition, SchemaDefinition};
 
@@ -47,3 +47,10 @@ impl<'a> Directive<'a> {
         self.arguments().find(|arg| arg.name() == name)
     }
 }
+
+impl<'a> InputObjectDefinition<'a> {
+    pub fn is_one_of(&self) -> bool {
+        self.directives()
+            .any(|directive| directive.name() == "oneOf")
+    }
+}