[canvaskit] Add float color support to ColorFilter.MakeBlend

Followup to https://skia-review.googlesource.com/c/skia/+/566445

This removes the conversion from float color to int color and
adds an optional colorspace param.

Change-Id: Ie9c7bf8e3edc31cb913fbd5314f9b8fd5aa4b4d2
Bug: skia:13637
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/567437
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
5 files changed