SI-6355 SI-7059 it is possible to overload applyDynamic

As our discussion at https://issues.scala-lang.org/browse/SI-6355 shows,
it looks like it is possible to overload applyDynamic, even though a
straightforward way is closed. This commit codifies the pattern proposed
by @paulp and makes sure that it doesn’t break in the future.
Merge pull request #3310 from xeno-by/topic/overload-dynamic

SI-6355 SI-7059 it is possible to overload applyDynamic
codifies the state of the art wrt SI-8104

As it was discovered in SI-8104, whiteboxity doesn’t apply equally to
type parameters and type members of materialized type classes.

During implicit search and subsequent type inference, whitebox type parameters
are consistently erased to wildcards, whereas whitebox type members sometimes
remain as is and get in the way of signature conformance checks.
Merge pull request #3311 from xeno-by/topic/fine-points-of-whiteboxity-master

(master) codifies the state of the art wrt SI-8104