Refactor ABIArgInfo::Expand implementation (NFC).

Hoist the logic which determines the way QualType is expanded
into a separate method. Remove a bunch of copy-paste and simplify
getTypesFromArgs() / ExpandTypeFromArgs() / ExpandTypeToArgs() methods.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218615 91177308-0d34-0410-b5e6-96231b3b80d8