Fix compile error for native debug build (#26248)
Fix compile error for native debug build (#26248)

Summary:
Fix Android gradle build error for native debug build.
`NATIVE_BUILD_TYPE=Debug ./gradlew :ReactAndroid:installArchives`
The root cause is `folly::Future<bool>` not declared.
As we don't include true folly::Future implementation in OSS build but to use a forward declaration,
the fix is pretty much like to original declaration as `folly::Future<folly::Unit>`.

## Changelog

[Android] [Fixed] - Fix compile error for native debug build
This change could be ignored from changelog which is only for internal development.
Pull Request resolved: https://github.com/facebook/react-native/pull/26248

Test Plan: Makes sure `NATIVE_BUILD_TYPE=Debug ./gradlew :ReactAndroid:installArchives` build without errors.

Differential Revision: D17169696

Pulled By: mdvacca

fbshipit-source-id: 42e8b84b7ee0d1bd99d913702df98bc030965f63

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