Move xplat/sonar/xplat/Sonar* to Flipper*

Summary:
Part of the Sonar -> Flipper rename
Intentionally left externally visible buck target as Sonar for now to minimize diff size.

Reviewed By: passy

Differential Revision: D9871684

fbshipit-source-id: 6926eb62c578a05cd895745c75ed7da3cfe965b5

xplat/Flipper/Log.cpp

@@ -0,0 +1,20 @@
+#include "Log.h"
+
+#ifdef __ANDROID__
+#include <android/log.h>
+#endif
+
+namespace facebook {
+namespace flipper {
+
+  void log(const std::string& message) {
+  #ifdef __ANDROID__
+    __android_log_print(ANDROID_LOG_INFO, "sonar", "sonar: %s", message.c_str());
+  #else
+    printf("sonar: %s\n", message.c_str());
+  #endif
+  }
+
+
+} // namespace flipper
+} // namespace facebook