layers: Get rid of pre-call updates in AllocateDescriptorSets
layers: Get rid of pre-call updates in AllocateDescriptorSets

Moving all the updates later requires that we totalize the required
descriptors by type first, rather than testing each binding's
requirement as we go.

Signed-off-by: Chris Forbes <c3279c50043e18e9442c1ae071cafa0e7a4ca967@google.com>

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools