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