Type the quoted patterns as precisely as possible

[nicolasstucki]

In a pattern match where the contents of the quote are statically known we want to propagate the
type inside the pattern the the binding. For example e will not only be an Expr[T] but also
an Expr[Some[Int]].

(s: Expr[T]) match {
  case e @ '{ Some($x: Int) } =>
    // e: Expr[T & Some[Int]]
    // x: Expr[Int]
}

If the expression in the pattern contains a spliced expression, possibly typed, we also need to propagate the
type of the scrutinee down into the pattern. For example x will not only be an Expr[Boolean] but also
an Expr[T].

(s: Expr[T]) match {
    case e @ '{ $x: Boolean } =>
      // e: Expr[T & Boolean]
      // x: Expr[T & Boolean]
}

[odersky]

Otherwise LGTM