Support for map of string keys to uint64_t / double values in RTCStats

Bug: webrtc:10685
Change-Id: I047d784bd20c3fca8b96391653f90fd8803140d8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/219141
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34121}

sdk/android/api/org/webrtc/RTCStats.java

@@ -62,6 +62,7 @@ public class RTCStats {
    * - Double
    * - String
    * - The array form of any of the above (e.g., Integer[])
+   * - Map of String keys to BigInteger / Double values
    */
   public Map<String, Object> getMembers() {
     return members;