WebGPU pipeline samples will break Engine

[Moriy]

If I set samples in DefaultRenderingPipeline (WebGPU) , webgpuEngine will break, throw 500+ warning and not display.
Not set samples (40+ warning, display normally):

If I set samples 2(500+ warning, display white):

[Evgeni_Popov]

This PR will fix the problem:

WebGPU: fix sampleCount value

In the meantime, you can use 4 instead of 2 as the samples value (WebGPU only supports 1 or 4).