In the rare case where vertex attribute buffers are bound to MVKCommandEncoder,
are not used by first pipeline, but are used by a subsequent pipeline, and no
other bindings are changed, the MVKResourcesCommandEncoderState will not appear
to be dirty to the second pipeline, and the buffer will not be bound to Metal.
When reverting a binding to dirty if it is not used by a pipeline, also revert
the enclosing MVKResourcesCommandEncoderState to dirty state.
Update MoltenVK to version 1.2.6 (unrelated).
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