Port IconLayer to WebGPU

[Pessimistress]

For #9504

Change List

• Attribute.getBufferLayout() skip sub-attributes with invalid vertex formats
• IconLayer merge some attributes into an interleaved buffer (bindings exceeds maxVertexBuffers)
• Plumbing

[Pessimistress]

Not ready to merge - TextLayer is broken because it is not packing the correct instanceOffsets.

[ibgreen]

• I see you are running into the limited number of vertex buffers - it is quite inconvenient, stricter than WebGL.
• 8 vertex buffers + 10 storage buffers seems to be the limit even on recent macbook https://webgpureport.org/
• We can of course do something on the CPU side to interleave, but it really gets in the way of a simple GPU-buffer-based layer API.