Update musicroom Play selection status.

This makes the musicroom Play action compatible with sl2's reuse
of displayables.
Do not take transition state when a parameter changes.

When a parameter to a transition changes, we have a different
transition, so taking the state doesn't work - it means we will
be representing the state of a different transition.
Update screens once before we lock them down for a hide.

This matches 6.17 behavior, and it makes sense that a hiding screen
should show the data as of the time it was hidden.
Compat old screen language location.
iap: Add Purchase and Restore actions, get_store_name function.
doc: IAP.
doc: Various minor improvements.
Preserve nearest over subsurface operation.