layers: GH-909 level/layer Valid Usage checking

layers: GH-909 level/layer Valid Usage checking

Refactor subresourceRange.levelCount and subresourceRange.layerCount
checking from PreCallValidateCreateImageView() into a standalone
helper function ValidateImageSubrangeLevelLayerCounts() to facilitate
reuse below.

Add ValidateImageSubrangeLevelLayerCounts() to ValidateBarrier(), to
address GH-909.

This extends the reuse of Valid Usages 00768 and 00769, which are
already tagged as deserving new standalone Valid Usages.
This change is implemented such that it will be simple to modify for
new VUs, once they're available.

Also canonicalize function names passed as parameter to helper
function.

Change-Id: I8346a19e9b2c4df578334c2aebfb78e6492bd1d9