Special treatment for local symbols in TypeTreeMemberType

Avoids calling `thisType` on the owner if it is a term symbol,
which doesn't make much sense.

This method is used internally in tree factory methods that
create, e.g, a `DefDef` based on the info of a `Symbol`.
Now working: PartialFunc dependent on value class param type

I speculated that value classes might also be prone to the
fact that symbol substitution neglected `ClassInfoType#parents`.

This test case failes under 2.11.0-M6, but now works after the
recent fix to `SubstMap`.