Replace `int` with `simd` in `Mask` function naming?

[okaneco]

I've seen this come up as a stumbling block where these functions were interpreted as relating to signed integer bitmasks.

I think this change would make it more clear what these functions do, along with making it easier to discover them in an IDE or docs as the "obvious" name for these functions.

Before	After
from_int	from_simd
from_int_unchecked	from_simd_unchecked
to_int	to_simd

As for the naming convention, there's (unstable) precedence in std with the as_simd/as_simd_mut wrappers over align_to. I think the naming here should incorporate simd somewhere in these Mask functions even if it ends up as from_simd_int or from_int_simd.

[calebzulawski]

I'm in favor of this, it seems reasonable.