RCTSurface: Optional sync ShadowView/View registing
RCTSurface: Optional sync ShadowView/View registing

Summary:
See the comment in code.
If we on the main thread on registering time, we can/will break sequentiality of registering and mounting processes doing registration asynchronously.
We need this to make sync mouting eventually possible.

Reviewed By: fkgozali

Differential Revision: D7014176

fbshipit-source-id: 110ad5e5d86e3422eac15c3b1bdb29ae04acd7e6

hoangpham95/react-native,myntra/react-native,hammerandchisel/react-native,arthuralee/react-native,facebook/react-native,exponent/react-native,exponentjs/react-native,facebook/react-native,javache/react-native,myntra/react-native,janicduplessis/react-native,facebook/react-native,hammerandchisel/react-native,arthuralee/react-native,myntra/react-native,arthuralee/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,hammerandchisel/react-native,javache/react-native,exponent/react-native,janicduplessis/react-native,javache/react-native,hoastoolshop/react-native,hammerandchisel/react-native,pandiaraj44/react-native,janicduplessis/react-native,javache/react-native,hoangpham95/react-native,pandiaraj44/react-native,hoastoolshop/react-native,hoangpham95/react-native,exponentjs/react-native,myntra/react-native,exponent/react-native,arthuralee/react-native,exponent/react-native,myntra/react-native,facebook/react-native,facebook/react-native,pandiaraj44/react-native,myntra/react-native,exponentjs/react-native,exponentjs/react-native,javache/react-native,hoastoolshop/react-native,pandiaraj44/react-native,exponentjs/react-native,pandiaraj44/react-native,exponent/react-native,javache/react-native,javache/react-native,hoangpham95/react-native,janicduplessis/react-native,exponentjs/react-native,exponentjs/react-native,arthuralee/react-native,hoangpham95/react-native,exponent/react-native,exponent/react-native,pandiaraj44/react-native,hoangpham95/react-native,myntra/react-native,exponentjs/react-native,hammerandchisel/react-native,hoastoolshop/react-native,pandiaraj44/react-native,javache/react-native,hoastoolshop/react-native,janicduplessis/react-native,facebook/react-native,hammerandchisel/react-native,pandiaraj44/react-native,hammerandchisel/react-native,exponent/react-native,facebook/react-native,myntra/react-native,hoangpham95/react-native,hoastoolshop/react-native,hoastoolshop/react-native,facebook/react-native,janicduplessis/react-native,hammerandchisel/react-native,janicduplessis/react-native,hoastoolshop/react-native,hoangpham95/react-native,myntra/react-native