Track whether a local has a single definition, and if so, if it has
a reference type, try and update its type from the declared type to
a better type taken from the value being assigned to the local.

Obtain types for some of the 'short-lived' ref type temps that should
have a single definition. Use both the tree and the eval stack as sources
of type information (the latter can be phased out if/when all tree nodes
can return rich type information).

Refactor the code that sets or updates lvClassHnd into utilities
to provide better auditing of type flow and make the set/update process
a bit more rigorous.

Cleanup the code that passes argument values a bit by commoning redundant
argument lookup expressions.