Binding to zero-sized range of a buffer #686

Should we allow zero-sized ranges of buffers to be bound in bind groups?

Related to #546 on zero-sized buffers, but more complex.

From @kvark on that issue:

For zero-sized bindings, an investigation is needed to see:

• whether zero sizes are allowed, in which backends
• what alignment/minimum size requirements are in the backends
• whether there are operations that don't rely on the range at all, i.e. getting the size of the buffer from the shader.