Summary:
Fixes#21639 , seems we tried to fix this before, please see related `PR` like [D10392176](36507e4a3c), #18627, but they don't solve it totally.
[iOS] [Fixed] - Fix TextInput maxLength when insert characters at begin
Pull Request resolved: https://github.com/facebook/react-native/pull/23472
Reviewed By: mmmulani
Differential Revision: D14366406
Pulled By: ejanzer
fbshipit-source-id: fc983810703997b48824f84f2f9198984afba9cd