[OpenMP] Tear down GenericDeviceTy's with GenericPluginTy (#73557)

There is no point in keeping GenericDeviceTy objects alive longer than
the associated GenericPluginTy. Instead of the old API we now tear them
down with the plugin, avoiding ordering issues.

GitOrigin-RevId: 7bfcce3e940f401a519906ecad3632978ccd0fb5
6 files changed