API refactor

[Daft-Freak]

Split the API struct into a "const" and "data" part. This is a result of me not wanting to reserve 2K of RAM on pico. After this, all the function pointers can be constants (may improve #484) and the data part only needs 64 bytes.

For compatibility, 32blit-stm32 is still using the old layout by inserting padding and overlaying the two structs on top of each other.

These are (I think) the only remaining non-pico changes on my big pico branch.

[Gadgetoid]

In hindsight this makes an awful lot of sense.

[Daft-Freak]

Fixed warnings from these patches being older than can_launch and needed to rebase for recent build fixes.

I'll have to add the STM32 nastiness to the list of things that can be cleaned up if there's an API break... (Also, I should actually write that list)