Metrics: Dump Java and native metrics together

* Both Java and native metrics are dumped when calling
  "dumpsys bluetooth_manager --proto-bin".
* "dumpsys bluetooth_manager --proto-java-bin" will always dump an empty
  protobuf after this change.
* Native metrics is dumped directly to Java layer as a byte array that can be
  directly merged to Java BluetoothLog.
* Native layer initially dumps metrics as std::string. The content of
  std::string is copied to Java layer as byte array

Bug: 33693818
Test: adb shell dumpsys bluetooth_manager --proto-bin
      SL4A metrics tests: BtMetricsTest, BtFunhausMetricsTest
Change-Id: I89d8f283f5d9d2145f80c6878fd0896fa5e7dafb