[native] Add @react-navigation/drawer

Summary:
This diff adds the package to package.json, and also introduces a Flow libdef.

Our other React Navigation libdefs were updated for React Nav 6 as part of ENG-336, but since we didn't use Drawer at the time I didn't update that one fully.

The Flow libdef here has SECTION 1 copy-pasted from the other React Nav 6 libdefs, but SECTION 2 is from the old React Nav 5 libdef currently on flow-typed. I'll update SECTION 2 based on the changelog in a subsequent diff, but since it looks like the old libdef for React Nav 5 was fairly incomplete, we'll likely need further updates.

Test Plan: Flow

Reviewers: atul, inka, tomek

Reviewed By: atul, tomek

Subscribers: abosh

Differential Revision: https://phab.comm.dev/D5537