Use new JavaScriptCore from npm (#22231)

Summary:
Pull Request resolved: facebook/react-native#22231

- Use clang instead of the deprecated gcc
- Use libc++ instead of the deprecated gnustl
- Updated gradle and android plugin version
- Fixed missing arch in local-cli template
- `clean` task should now always succeed
- `clean` task deletes build artifacts
- No need to specify buildToolsVersion. It's derived.
- Elvis operator for more readable code
Pull Request resolved: facebook/react-native#22263

Reviewed By: hramos

Differential Revision: D13004499

Pulled By: DanielZlotin

fbshipit-source-id: da54bb744cedb4c6f3bda590f8c25d0ad64086ef

Author: DanielZlotin

android/app/build.gradle

@@ -92,7 +92,6 @@ def enableProguardInReleaseBuilds = true
 
 android {
     compileSdkVersion 28
-    buildToolsVersion "28.0.2"
 
     defaultConfig {
         applicationId "com.facebook.react.uiapp"