(0.62) Exception thrown any time pickers are imported

[NickGerleman]

We see an invariant violation on pages with pickers due to RCTPicker being registered twice. We've seen a similar issue during the 0.62 upgrade for ScrollView that required taking in some new JS-side changes for code that only happens off of Android/iOS.

[NickGerleman]

Looks like this is actually just for PickerWindows/DatePicker. Root cause is simply requiring RCTPicker in multiple files. Should be an easy fix.