This isn't a complete conversion to ErrorOr<void>, but a good chunk.
The end goal here is to propagate buffer allocation failures to the
caller, and allow the use of TRY() with formatting functions.
This introduces a new MovementType concept to LibCards, starting the
process to allow other patience games to be implemented using it - that
differ more substantially from Klondike in logic.
This is currently used for two purposes: 1. to verify that the
'grabbed' stack of cards is valid* (sequential and correct colours) and
2. to allow 'grabbed' stacks to be pushed onto same-colour,
either-colour, or alternating-colour stacks
* Klondike doesn't need this logic, as per how the game works any
'grabbed' selection is guaranteed to be valid.
Now that the cards have rounded corners, draw the stack box behind the
cards with rounded corners as well. This way, the corner of the stack
box doesn't peek out from behind the cards.
The caveat here is that the "play" card stack now needs to hold a
reference to the "waste" stack beneath it so it knows when not to draw
its background on top of the waste stack. To faciliate that, the array
of card stacks is now a NonnullRefPtrVector so the play stack can store
a smart pointer to the waste stack (instead of a raw pointer or
reference).
