[native] Add isAnimatingToSidebar flag to a hook value
[native] Add isAnimatingToSidebar flag to a hook value

Summary: We need this to decide how we will animate a tooltip header opacity: when we navigate to a sidebar, the lower end of opacity is going to be different.

Test Plan: Use console log to check if the returned value is correct.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D1856

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