mGBA shaders accuracy issues

[GrieverV]

Both GLSL and Slang versions of ags001 shaders have inaccuracies

mGBA

RetroArch GLSL

1. In the first image, notice the dark bar at the top in RetroArch which isn't present in mGBA
2. In the second image, notice how the reflection is completely different than mGBA
3. In the second image, notice how there's a black square in the center which fades out slightly. The bottom of the square appears to extend past the screen in RetroArch.

Slang does not suffer from #3 and the reflection is similar to RA GLSL but the strength is closer to mGBA. agb001 shader was not tested.

@Monroe88 according to git you were the original committer for these shaders so this issue may interest you.