Add differential privacy library and algorithms

- Created a differential privacy framework interface
- Added 2 DP algorithms in DP framework:
  -  Rappor, a wrapper based on external/rappor project
  -  Longitudinal Reporting, DP enhancement based on Rappor
- Created Privacy Tests for testing all privacy libraries
- Added original Rappor test case in privacy test
- Created tests to verify Rappor and Longitudinal Reporting result in DP framework

Test: bit FrameworksPrivacyLibraryTests:android.privacy.LongitudinalReportingEncoderTest
Test: bit FrameworksPrivacyLibraryTests:android.privacy.RapporEncoderTest

Change-Id: Id460665059653924434c141686b5cad3fb697046
diff --git a/Android.bp b/Android.bp
index 979ed1c..80eaa7d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -671,6 +671,7 @@
         "libphonenumber-platform",
         "nist-sip",
         "tagsoup",
+        "rappor",
     ],
     dxflags: ["--core-library"],
 }