fix(filter): pixelate behaves differently under webgl, and should be squares rather than image scale

[xushengfeng]

Description

In Pixelate.applyTo2d, Pixels are squared, which is consistent with the expected performance
But in webgl, pixels follow the width and height of the image.

In Action

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[asturur]

i remember noticing this and for some reason i thought i fix it, eventually i didn't.

[asturur]

Can you post a screenshot of a non square image after pixelate filter is applied? thank you

[xushengfeng]

https://jsfiddle.net/5vojyagL/5/

a 200*100 gradient as an example photo

[asturur]

This is with your fix or without?

[xushengfeng]

the fiddle example is 6.3.0 which isnot fixed

I applied the changes I made in the pull directly in index.min.mjs and it worked fine. I believe this pull change also applies to the source code (because the characters of this change are not affected by compilation)

[asturur]

This is good to merge, it would be nice to add a visual test for regressions and a changelog.
The changelog you can figure out by looking at the changelog.MD file, for the test i can do it as soon as i have some minute free