Make getClassGClayout work with with class types.
Make getClassGClayout work with with class types.

Also add an assert to getHeapClassSize to ensure it's not
called in R2R cross-version-bubble.

mmitche/coreclr,wtgodbe/coreclr,poizan42/coreclr,wtgodbe/coreclr,cshung/coreclr,mmitche/coreclr,krk/coreclr,krk/coreclr,mmitche/coreclr,poizan42/coreclr,wtgodbe/coreclr,cshung/coreclr,wtgodbe/coreclr,cshung/coreclr,mmitche/coreclr,poizan42/coreclr,wtgodbe/coreclr,cshung/coreclr,krk/coreclr,cshung/coreclr,krk/coreclr,poizan42/coreclr,mmitche/coreclr,mmitche/coreclr,poizan42/coreclr,krk/coreclr,poizan42/coreclr,cshung/coreclr,krk/coreclr,wtgodbe/coreclr