textsize/fontsize inconsistency

[KronosTheLate]

When setting a theme, one uses the kwarg fontsize.
When creating a Label, one uses the kwarg textsize.

They each give the most sense in their current context, but I feel that it is the opposite of user-friendly to have these two things, which mean the same from the user-perspective, to have different kwargs.

Because changing a kwarg is breaking, I suggest that the two kwargs should give the same result in both contexts, aka be aliases of eachother.

[andrewwinters5000]

I think that this can be resolved as the textsize keyword argument has been removed in #2387