Add crossfade transition

[Revxrsal]

This PR adds a basic crossfade transition for navigation, as I felt it's missing.

[DevNatan]

Binary compatibility check failed please run gradle apidump to regenerate .api with your code. Also, can you provide a GIF using this transition on one of our samples, for us to include in the docs

[Revxrsal]

I made the function public. I've tried running gradle apidump, but it gave me an error about local.properties missing. I admittedly feel it's unnecessary to go through the whole setup procedure and install what's probably worth 1GB+ dependencies for all the platforms that Voyager supports, just to add a simple function 😅

Here's a GIF:

[Revxrsal]

Hey @DevNatan o/ I know you're busy, but could you please let me know if anything's left here? I use voyager in so many projects and this would save me lots of time 🙆‍♂️