vello_gpu: Optimize full-sized texture sampling

[laurenz-canva]

This PR adds a fast path for images where we want to sample the whole texture. When this is the case, we can make use of WebGL sampler objects to define whether to use NN/bilinear sampling as well as which extend mode to use, without us having to reimplement these operations in software! This is much faster, see this video and compare to the FPS numbers from #1963 instead:

IMG_1298.MOV

The only two downsides are that

1. It makes our shaders even bigger.
2. We need to reject non-filterable textures, which I don't think is a big deal for now. In the future, we can refine this so non-filterable textures are accepted again, as long as the user only uses ImageQuality::Low.

Once this (and the preceding PR) have been approved, I will make sure to rerun tests on other devices to ensure we are not creating any regressions by making the shader bigger.

[LaurenzV]

In theory, we could derive that information ourselves using textureDimensions in the shader. However, I faintly remember this being a performance footgun. Hence why I think it's better to require that information to be passed along.

[LaurenzV]

Bit annoying to abuse the payload like this. 😅 But it avoids having to do another texture sample in the fragment shader, as all the metadata we need is passed directly.

[LaurenzV]

TODO: Use textureSample?