Add is_required / is_repeated properties to FieldDescriptor (#14703)

stubs/protobuf/google/protobuf/descriptor.pyi

@@ -156,6 +156,10 @@ class FieldDescriptor(DescriptorBase):
     @property
     def label(self): ...
     @property
+    def is_required(self) -> bool: ...
+    @property
+    def is_repeated(self) -> bool: ...
+    @property
     def camelcase_name(self) -> str: ...
     @property
     def has_presence(self) -> bool: ...