Restructure track selection in DashMediaPeriod.

Until now, the streams were released and re-enabled for each type of stream
(primary, event, embedded) in that order. That leads to problems when replacing
streams from one type to another (for example embedded to primary).

This change restructures the track selection to:
1. Release and reset all streams that need to be released or replaced.
 1(a). Including embedded orphan streams.
2. Select new streams.

Issue:#4477

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=203751233

RELEASENOTES.md

@@ -21,6 +21,8 @@
 * Add workaround for track index mismatches between tfhd and tkhd boxes in
   fragmented MP4 files
   ([#4083](https://github.com/google/ExoPlayer/issues/4083)).
+* Fix issue when switching track selection from an embedded track to a primary
+  track in DASH ([#4477](https://github.com/google/ExoPlayer/issues/4477)).
 
 ### 2.8.2 ###