Summary: Create isDeviceLanguageRTL function to connect the OS language with isRTL. Now even if a new app could support RTL language, without setting forceRTL at JS side it won't directly change into RTL layout.
Reviewed By: fkgozali
Differential Revision: D3473109
fbshipit-source-id: ac1410c910e980d44750bb88cad7615febb9e076