[DocsUI Peek] Clear preview handler on destroy view

Observed bug: The exoplayer's resources were not released on
configuration change. Its `release` method needs to be explicitely
called. More generally, make sure that the previewHandler's clear method
is called, not only when Peek gets hidden, but also in `onDestroyView`.

Bug: 382169786
Flag: com.android.documentsui.flags.use_material3
Flag: com.android.documentsui.flags.use_peek_preview_ro
Test: Manually checked that audio stops playing on configuration change
Change-Id: I10517c575622f31f117c3029b6ac9c6917fbfa30