Support for Integer vertex attributes on WebGL2

[mvaligursky]

Fixes #3930

• Int/uint attributes are now supported - which makes them available in shader as int/uint numbers, instead of as floats.
• This is also used on Splats, WebGL2 uses integer splat IDs to match WebGPU. Only WebGL1 uses floats.

New API

• VertexFormat.description[].asInt - true to interpret as int attribute, false as float (default)

example:

        const vertexFormat = new VertexFormat(device, [
            { semantic: SEMANTIC_ATTR13, components: 1, type: TYPE_UINT32, asInt: true }
        ]);