Change the canonical representation of array types to store qualifiers on the

outermost array types and not on the element type.  Move the CanonicalType
member from Type to ExtQualsTypeCommonBase;  the canonical type on an ExtQuals
node includes the qualifiers on the ExtQuals.  Assorted optimizations enabled
by this change.

getQualifiers(), hasQualifiers(), etc. should all now implicitly look through
array types.

llvm-svn: 123817