Optional XY manual fade mode

[bobbadshy]

When the use case is to save presets for several XY faders, maybe it makes sense to add an optional manual fade mode that uses an XY pad, so you can manually fade both values independently.

It might not go well performance-wise though ..and this is also maybe kind of abusing the preset module for something it's not really meant for, and this might be better implemented by having a dedicated "fade all" XY pad on the respective surface, and just use that instead of a preset fade..?