Update media3 to 1.2.1

[ziad-halabi9]

This update is required to fix a Dolby Atmos issue that was fixed in version 1.2.1.

Change log here.

A lot of APIs are now marked as @UnstableApi. Do we prefer to suppress per-case as done in this PR or globally suppress them?

[stoyicker]

my preference would be

1. understanding why everything is marked like this so we can decide if we need to do something about it
2. individual suppress
3. global suppress

then again, potato potato

[ziad-halabi9]

For their demos and libraries, they suppress it by adding lint.xml:

<?xml version="1.0" encoding="utf-8"?>
<lint>
  <issue id="UnsafeOptInUsageError">
    <option name="opt-in" value="androidx.media3.common.util.UnstableApi" />
  </issue>
</lint>

File: https://github.com/androidx/media/blob/release/libraries/lint.xml

So alternatively we can do the same: #110

I see these @UnstableApi has always been there (prior to v1.2.1) but the way they were suppressed have changed and hence why we see this issue now.