Streamline legacy gradient color conversion

To produce colors for interpolation in legacy mode, we currently do
something like

  SkColor c = Sk4f_toS32(swizzle_rb(Sk4f::Load(c4f)));
    color4f = swizzle_rb(SkNx_cast<float>(Sk4b::Load(&c)) * (1/255.0f));

Let's see if we can streamline some of that.

Change-Id: I423b5aa8c2df8d115cc236d5f0a2e79923a9c2cc
Reviewed-on: https://skia-review.googlesource.com/66142
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed