Fix non-dismissible resumption players.

Ensure resumption players created when a non-dismissible notification is cancelled
force the 'isClearable' flag to true. This fixes a bug where a resumption player is
non-dismissable.

Test: manual - Finish episode in Pocket Casts, attempt long-press dismiss.
Bug: 169271494
Change-Id: I186f9ee6fc228ad5bd1d49970fb44709783b74dc