Fix multi-period transitions with track selection overrides

An override applies across periods provided they expose the
same track groups according to .equals, but the formats in
the override are then compared against the period's formats
according to ==. Use .equals consistently to fix.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=129081591

library/src/main/java/com/google/android/exoplayer2/source/TrackGroup.java

@@ -67,7 +67,7 @@ public final class TrackGroup {
    */
   public int indexOf(Format format) {
     for (int i = 0; i < formats.length; i++) {
-      if (format == formats[i]) {
+      if (formats[i].equals(format)) {
         return i;
       }
     }

library/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java

@@ -58,7 +58,7 @@ public final class TrackGroupArray {
    */
   public int indexOf(TrackGroup group) {
     for (int i = 0; i < length; i++) {
-      if (trackGroups[i] == group) {
+      if (trackGroups[i].equals(group)) {
         return i;
       }
     }

library/src/main/java/com/google/android/exoplayer2/trackselection/BaseTrackSelection.java

@@ -100,7 +100,7 @@ public abstract class BaseTrackSelection implements TrackSelection {
   @Override
   public final int indexOf(Format format) {
     for (int i = 0; i < length; i++) {
-      if (formats[i] == format) {
+      if (formats[i].equals(format)) {
         return i;
       }
     }