Summary:
Currently Android fails to build on Windows, because CMake cannot work with
native Windows paths that are passed to it as build arguments. This change
converts the input paths to the CMake format.

## Changelog:

[Android] [Fixed] - Fix building Android on Windows.

Pull Request resolved: https://github.com/facebook/react-native/pull/39190

Test Plan: Build the React Native Android project on Windows. It should complete successfully.

Reviewed By: NickGerleman

Differential Revision: D48948140

Pulled By: cortinico

fbshipit-source-id: 6d584c2a10e683cdb6df0dd6dcd5875da7e06e2b