Fix #3636: Better disambiguation in withPrefix

[odersky]

Use the kind of disambiguation in withPrefix that we apply already in memberDenot.

[liufengyun]

LGTM.

There's one thing I don't quite understand: is it safe to do overloading resolution for inlined names? Is it possible that an inlined name during overloading resolution gets bound to another symbol?

[odersky]

There's one thing I don't quite understand: is it safe to do overloading resolution for inlined names? Is it possible that an inlined name during overloading resolution gets bound to another symbol?

For inlining, they are always the same symbol, since the new prefix has the same widened type as the original one. But the mechanism we are using for inlining (TreeTypeMaps, which use in turn withPrefix) can rebind symbols. We could have fixed the problem by fixing the symbol explicitly when inlining. But I thought it was better to make the underlying mechanism better at disambiguating.