Fix Vulkan MEC image element size for stencil/depth (#3205)
Fix Vulkan MEC image element size for stencil/depth (#3205)

subGetDepthElementSize() should be used only for the DEPTH aspect, not
the STENCIL aspect.
google/agi,google/agi,google/gapid,pmuetschard/gapid,google/agi,pmuetschard/gapid,google/agi,google/agi,pmuetschard/gapid,google/agi,google/gapid,google/gapid,google/gapid,google/agi,pmuetschard/gapid,google/gapid,google/agi,google/gapid,pmuetschard/gapid,google/gapid,pmuetschard/gapid,pmuetschard/gapid,pmuetschard/gapid,google/gapid