Currently FirThisReceiverExpression of instance methods are translated
to references of the class' thisReceiver,
not the method's dispatch receiver,
which causes problems with IrFrameMap::typeOf,
as the class' thisReceiver is not in the typeMap.
This commit translates non-qualified "this" references of
instance methods to references of the methods' dispatch receiver.
If 'this' (implicit or explicit) was used as an extension receiver,
and the corresponding call required a smart-cast,
this information was effectively lost in "old" resolution & inference,
but is required by "old" JVM BE to generate proper CHECKCASTs.
Juan Chen