Add validation in accordance with WebGPU setViewport valid usage fo…

[James2022-rgb]

…r x, y and this.[[attachment_size]].

x and y must not be negative, and the rect must be contained in the render target.

Checklist

• Run cargo clippy.
• Run cargo clippy --target wasm32-unknown-unknown if applicable.
  Done just in case, with --feature gles.
• Add change to CHANGELOG.md. See simple instructions inside file.

Description
For wgpu::RenderPass::set_viewport, it was possible to use values such that:

• x and/or y is negative
• the rect is not contained in the render target.

both of which are in violation of the valid usage defined for setViewport in the WebGPU spec:

x ≥ 0
y ≥ 0
x + width ≤ this.[[[attachment_size]]].width
y + height ≤ this.[[[attachment_size]]].height

This PR renames RenderCommandError::InvalidViewportDimension to InvalidViewportRect and adds render target extent to it, in the same spirit as InvalidScissorRect (which has similar valid usage regarding render target extent).

Testing
Tested locally.

[Wumpf]

nice and clean, thank you!