Remove `DeckSpinnerSelection` and recode `DeckSelectionDialog`

It's been a mess for years. We can do much better, especially now we're in Kotlin

This class originally existed because we had a spinner to select decks

This became `DeckSelectionDialog`, but the spinner remained.

This could be a spinner embedded in the App Bar, or a View in Note Editor.

Even if we keep a spinner control for the UI, the implementation is currently far too complex to justify it.

`CreateDeckDialog` was then added into `DeckSelectionDialog`, so in some instances, the calling activity needs to handle a newly created deck from this dialog.