Refactor alphablit

[MightyJosip]

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Current alphablit has way too many repetitive code. For example, in each blend blitter, around 90% of the code is the same. So I decided to move it into the macro, and by that, reduce the file by around 40% of the lines.

The good side of this commit is that if we do eventual change on the blitter code, we only need to do it in the one place, the code became more modular. However, macros probably make the code harder to read, so we need to decide will we proceed with this change