Replace `s.c.MapOps.filterKeys` with `s.c.MapOps.view.filterKeys`

/** Filters this map by retaining only keys satisfying a predicate.
  *  @param  p   the predicate used to test keys
  *  @return an immutable map consisting only of those key value pairs of this map where the key satisfies
  *          the predicate `p`. The resulting map wraps the original map without copying any elements.
  */
@deprecated("Use .view.filterKeys(f). A future version will include a strict version of this method (for now, .view.filterKeys(p).toMap).", "2.13.0")
def filterKeys(p: K => Boolean): MapView[K, V] = new MapView.FilterKeys(this, p)