Mangling a non-canonical type can run into
unexpected type sugar such as the newly introduced
LocatableType. USRs should be based on canonical
types anyway, so make sure we canonicalize before
mangling.
rdar://141168628
Typically, users jump to type-specific interface from a member of that type, for
instance, a.getSomething(). To generate the interface, we need to report the USR
of the container type of "getSomething()", which is the USR for the type of a,
when cursor info is requested for this function call.
