Fix $FlowFixMe in Flatlist
Fix $FlowFixMe in Flatlist

Summary:
$FlowFixMe suppressed type validation on _listRef. Add appropriate typing to let Flow succeed when $FlowFixMe is removed.

Not sure what this project's philosophy around ref types is. In some places I've seen them annotated as any rather than trying to get a more granular type to match. I'm open to suggestions.

`yarn flow`

[INTERNAL] [ENHANCEMENT] [FlatList.js] - Remove $FlowFixMe from FlatList
Closes https://github.com/facebook/react-native/pull/16882

Differential Revision: D6386479

Pulled By: hramos

fbshipit-source-id: bed14f2c7071525cb46425ab14214771de0277f3

arthuralee/react-native,hoastoolshop/react-native,hoangpham95/react-native,javache/react-native,janicduplessis/react-native,ptmt/react-native-macos,myntra/react-native,myntra/react-native,arthuralee/react-native,exponentjs/react-native,hoastoolshop/react-native,janicduplessis/react-native,dikaiosune/react-native,exponent/react-native,hammerandchisel/react-native,hammerandchisel/react-native,ptmt/react-native-macos,exponent/react-native,hoangpham95/react-native,rickbeerendonk/react-native,myntra/react-native,exponent/react-native,rickbeerendonk/react-native,hammerandchisel/react-native,Bhullnatik/react-native,facebook/react-native,janicduplessis/react-native,pandiaraj44/react-native,hoangpham95/react-native,jevakallio/react-native,pandiaraj44/react-native,hammerandchisel/react-native,exponent/react-native,rickbeerendonk/react-native,myntra/react-native,hoangpham95/react-native,exponent/react-native,hoangpham95/react-native,facebook/react-native,pandiaraj44/react-native,facebook/react-native,janicduplessis/react-native,myntra/react-native,exponent/react-native,ptmt/react-native-macos,Bhullnatik/react-native,jevakallio/react-native,dikaiosune/react-native,hoangpham95/react-native,myntra/react-native,hoastoolshop/react-native,javache/react-native,javache/react-native,Bhullnatik/react-native,exponentjs/react-native,javache/react-native,ptmt/react-native-macos,rickbeerendonk/react-native,javache/react-native,kesha-antonov/react-native,kesha-antonov/react-native,hoastoolshop/react-native,janicduplessis/react-native,Bhullnatik/react-native,hammerandchisel/react-native,rickbeerendonk/react-native,dikaiosune/react-native,dikaiosune/react-native,hoangpham95/react-native,hoastoolshop/react-native,hoangpham95/react-native,jevakallio/react-native,kesha-antonov/react-native,kesha-antonov/react-native,arthuralee/react-native,kesha-antonov/react-native,kesha-antonov/react-native,janicduplessis/react-native,javache/react-native,dikaiosune/react-native,Bhullnatik/react-native,ptmt/react-native-macos,exponentjs/react-native,arthuralee/react-native,pandiaraj44/react-native,exponent/react-native,myntra/react-native,hammerandchisel/react-native,rickbeerendonk/react-native,hammerandchisel/react-native,kesha-antonov/react-native,myntra/react-native,jevakallio/react-native,facebook/react-native,exponentjs/react-native,exponent/react-native,facebook/react-native,ptmt/react-native-macos,exponentjs/react-native,jevakallio/react-native,rickbeerendonk/react-native,dikaiosune/react-native,myntra/react-native,ptmt/react-native-macos,pandiaraj44/react-native,jevakallio/react-native,pandiaraj44/react-native,jevakallio/react-native,rickbeerendonk/react-native,hoastoolshop/react-native,ptmt/react-native-macos,facebook/react-native,Bhullnatik/react-native,hammerandchisel/react-native,facebook/react-native,kesha-antonov/react-native,dikaiosune/react-native,javache/react-native,jevakallio/react-native,rickbeerendonk/react-native,hoastoolshop/react-native,hoastoolshop/react-native,dikaiosune/react-native,janicduplessis/react-native,exponentjs/react-native,exponentjs/react-native,exponentjs/react-native,jevakallio/react-native,javache/react-native,facebook/react-native,pandiaraj44/react-native,facebook/react-native,javache/react-native,arthuralee/react-native,pandiaraj44/react-native,janicduplessis/react-native,Bhullnatik/react-native,Bhullnatik/react-native,kesha-antonov/react-native