Fixed Period Transition

[Redirion]

What is it?

• Bugfix (user facing)
• Feature (user facing)
• Codebase improvement (dev facing)
• Meta improvement to the project (dev facing)

Description of the changes in your PR

I missread the ExoPlayer 2.14.0 changelog
Report information about the old and the new playback positions to Listener.onPositionDiscontinuity. Add DISCONTINUITY_REASON_SKIP and DISCONTINUITY_REASON_REMOVE as discontinuity reasons, and rename DISCONTINUITY_REASON_PERIOD_TRANSITION to DISCONTINUITY_REASON_AUTO_TRANSITION. Remove DISCONTINUITY_REASON_AD_INSERTION, for which DISCONTINUITY_REASON_AUTO_TRANSITION is used instead

particularly as REASON_AD_INSERTION was replaced by REASON_AUTO_TRANSITION I replaced this in our code. However as PERIOD-TRANSITION was changed to AUTO_TRANSITION we lost the previous behaviour. Stupid me.
This commit fixes the ExoPlayer 2.14.2 PR #7005

I am a bit unsure if DISCONTINUITY_REASON_REMOVE should be at the same position, but according to the javadoc it should be, so I would leave it there unless anyone has objections.
I have checked the ExoPlayer Sourcecode, for me it looks like this is okay there.

APK testing

The APK can be found by going to the "Checks" tab below the title. On the left pane, click on "CI", scroll down to "artifacts" and click "app" to download the zip file which contains the debug APK of this PR.

Due diligence

• I read the contribution guidelines.

[litetex]

LGTM

Scrolled a bit inside the player, tested background and popup player.
Seems as everything is working as expected.