3D rendering backend implementation

[slimsag]

general issue for tracking this + notes related to it

[slimsag]

from the Dawn matrix chat - avoid the default pipeline layouts:

[slimsag]

useful info about querying max vertex attributes limit:

I think we started enforcing this differently at some point. The corresponding limit is maxVertexAttributes.

The discussion for this change is here gpuweb/gpuweb#1418

We decided that the attribute locations had to be under the max number of attributes, at least for now.

I think this is maxInterStageComponents.
We added a limit to the number of "varyings"