[Flow202][native][skip-ci] [47/x] Parameterize StyleSheet.flatten invocations
Summary:
Separating this out because I made some opinionated changes in Markdown. I don't think we need to import FlattenedTextStyle anymore because Flow is able to deduce the types automatically based on the type param.
NOTE: CI will fail on this diff. I considered the possibility of fixing Flow errors BEFORE upgrading Flow, but it wasn't possible... in some cases, the fixes to support the new version of Flow caused errors in the old version. I could have hidden these type errors with $FlowFixMe lines and then later revert those, but that seemed like too much busy work.
Depends on D10030
Test Plan: Confirm the Flow errors go away
Reviewers: ginsu
Reviewed By: ginsu
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D10031