core: use ColorMixin for colors

[Rainrider]

Closes #590

No BC breaks. I'll switch elements and stuff if you want this. Just left them in for now to demonstrate BC.

[p3lim]

LGTM

[p3lim]

If you want to update everything else to use :GetRGB() and whatnot that's up to you, but it'll eventually be something we'll want to do.

This probably also involves updating the color-related APIs oUF exposes, but they can probably be left alone unless there are performance reasons to update them.

[Rainrider]

Used following code for a perf benchmark where color is a local copy of Interface/SharedXML/Color.lua and Interface/SharedXML/Mixin.lua (only what is needed for the call to CreateFromMixins):

package.path = package.path .. ';./?.lua'

require('color')

local function benchmark(times, name, f, ...)
	local start = os.clock()
	for i = 1, times do
		f(...)
	end
	local elapsed = (os.clock() - start)

	print(('%16s: %9.3f ms'):format(name, elapsed * 1e4))
end

local r, g, b = 0.1, 0.4, 0.8
local color = CreateColor(r, g, b)
color[1] = r
color[2] = g
color[3] = b
color.atlas = 'some-atlas'

local color2 = { r, g, b, atlas = 'some-atlas' }

local function callRGB(color)
	local r, g, b = color:GetRGB()
end

local function callUnpack(color)
	local r, g, b = unpack(color)
end

local function getByIndex(color)
	local r, g, b = color[1], color[2], color[3]
end

local function getByName(color)
	local r, g, b = color.r, color.g, color.b
end

benchmark(1e6, 'color:getRGB()', callRGB, color)
benchmark(1e6, 'unpack(mixin)', callUnpack, color)
benchmark(1e6, 'index mixin', getByIndex, color)
benchmark(1e6, 'name mixin', getByName, color)
benchmark(1e6, 'unpack(simple)', callUnpack, color2)
benchmark(1e6, 'index simple', getByIndex, color2)
benchmark(1e6, 'name simple', getByName, color2)

Results:

  color:getRGB():   795.010 ms
   unpack(mixin):  1178.900 ms
     index mixin:   591.340 ms
      name mixin:   532.440 ms
  unpack(simple):   970.390 ms
    index simple:   689.990 ms
     name simple:   684.070 ms

So I kept the direct table access instead of calling color:GetRGB() but retrieve the color components by name rather than index. This allows us to ditch the array part in the next expac.

[p3lim]

👍