feat: Optimization in sprite batch

[erickzanardo]

Description

After a chat with the flutter team responsible for the rendering engine, I've learned that we don't need to pass a blend mode and colors for the drawAtlas call is those colors/blending will not generate any real change in the rendered result.

On SpriteBatch by default we add a full transparent color for all the rects in the batch, that blending makes no difference in the final rendered call since it is a transparent color, so we were adding unnecessary processing in the calls.

This PR changes SpriteBatch in a way that is had no default blending color and it will just pass those colors to drawAtlas if the developer has explicit informed a default color or a color in the render.

I made a quick benchmark and this optimization is minor, but still noticeable. To make it easier to notice the difference, in my game I forced the sprite batch render method to repeatedly render itself 100 times per render call. Without the changes, in my benchmark scenario these were taking an avg of 136 microseconds, while with the change, that time decreased to 100 microseconds.

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

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[spydon]

That is not a minor performance improvement with more than 20%, good job!