Move `Size` here?

[devmotion]

I wonder if it would be possible to move Size to this package? For instance, by moving (parts of) https://github.com/JuliaArrays/StaticArrays.jl/blob/ec2dc5ee8559e4d3125e4a392c050bfa27b8bfe1/src/traits.jl?

This was already discussed briefly in #3.
Size is currently mentioned in the docstring of similar_type even though it is not available in StaticArraysCore.
If it would be available also downstream code such as in JuliaDiff/DiffResults.jl#22 could be simplified.

[mateuszbaran]

Yes, I think that would be a good idea. I will try doing it today or tomorrow.