[native] Fix allowImagePasteForThreadID @property annotation

Summary: The @property annotation for allowImagePasteForThreadID was incorrect. It happened to work previously but now it has been fixed to allow pending threadInfo.id to correctly be passed to the objc side.

Test Plan: Tested by pasting images into pending threads and seeing if the ImagePasteModal appeared. Next step is making adjustments to the imagePastedCallback to correctly handle sending of messages.

Reviewers: ashoat, palys-swm

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian, subnub, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D734