fix: NativeImage.getScaleFactors returns correct scales

[nornagon]

Description of Change

Extracting part of #25727 which is safer (though doesn't fix everything that #25727 does).

gfx::ImageSkia::GetSupportedScales() is a static method that always returns the same values, regardless of the properties of the image.

Fixing this necessitated changing the CreateFromPNG function to call AddImageSkiaRepFromPNG instead of CreateFrom1xPNGBytes. The reason is that gfx::Image has some functionality for lazily decoding PNG images on an as-needed basis. When a gfx::Image is created with a PNG source, it will only materialize a representation (pixel buffer) for that image when a specific scale factor is requested. So asking for "what scale factors does this image have?" of an image created in this way, when no scale factors have already been requested, would return an empty list.

This has the downside that we now eagerly decode PNGs instead of lazily decoding them. Unfortunately, there is no way to detect the "lazy-decoding" state through the API that gfx::Image decodes. This PR chooses correctness over performance.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed NativeImage.getScaleFactors() always returning the same value.

[release-clerk]

Release Notes Persisted

Fixed NativeImage.getScaleFactors() always returning the same value.

[trop]

I have automatically backported this PR to "11-x-y", please check out #25903

[trop]

I have automatically backported this PR to "9-x-y", please check out #25904

[trop]

I have automatically backported this PR to "10-x-y", please check out #25905