[native] fix path to native rust library directory

Summary: We were incorrectly including a directory containing build artifacts from a previous Xcode build. This happened to work by coincidence, but is not the right directory. Now we include the directory created by corrosion containing the correct native_rust_library source files.

Test Plan: cd native/android && ./gradlew bundleDebug && ./gradlew bundleRelease

Reviewers: atul, jon, max

Reviewed By: atul, jon, max

Subscribers: ashoat, tomek, abosh, marcin, inka

Differential Revision: https://phab.comm.dev/D5480