MediaMetricsManagerService: Unify logSessionId representation

Use 96 bit integer / 16 char BaseURL representation.

Test: atest AudioTrackTest#testSetLogSessionId
Test: atest AudioRecordTest#testSetLogSessionId
Test: atest MediaRecorderTest#testSetGetLogSessionId
Test: atest MediaDrmTest#testPlaybackComponent
Bug: 193164585
Change-Id: I99a070f4ca4efb03416dff770c2a3a90d7ad2c58

services/core/java/com/android/server/media/metrics/MediaMetricsManagerService.java

@@ -195,7 +195,7 @@ public final class MediaMetricsManagerService extends SystemService {
         }
 
         private String getSessionIdInternal(int userId) {
-            byte[] byteId = new byte[16]; // 128 bits
+            byte[] byteId = new byte[12]; // 96 bits (128 bits when expanded to Base64 string)
             mSecureRandom.nextBytes(byteId);
             String id = Base64.encodeToString(
                     byteId, Base64.NO_PADDING | Base64.NO_WRAP | Base64.URL_SAFE);