Fix RNTester Lint errors

[friederbluemle]

Summary

Trying to build the Android RNTester app using Gradle fails with the following error:

  Errors found:
  
  [...]/RNTester/android/app/src/main/AndroidManifest.xml:2: Error: Hardware feature android.hardware.touchscreen not explicitly marked as optional  [ImpliedTouchscreenHardware]
  <manifest
   ~~~~~~~~
  [...]/RNTester/android/app/src/main/AndroidManifest.xml:2: Error: Expecting <uses-feature android:name="android.software.leanback" android:required="false" /> tag. [MissingLeanbackSupport]
  <manifest
   ~~~~~~~~

This PR adds the two missing uses-feature tags to AndroidManifest of RNTester.

Changelog

[Android] [Fixed] - Fix RNTester Lint errors

Test Plan

After adding the tags, the build is successful again.

[facebook-github-bot]

@mdvacca is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @friederbluemle in 1437510.

^{When will my fix make it into a release? | Upcoming Releases}