Implement tablet pressure support

[midwan]

Most of the tablet support from WinUAE is already in place, but some parts are still missing.
TODO: Implement the missing parts so we can have identical functionality in Amiberry.

[midwan]

It looks like this is only implemented in SDL3: https://wiki.libsdl.org/SDL3/CategoryPen

If that's the case, this issue will have to wait until support for SDL3 is implemented in Amiberry.