Fix level checking for this.type in macros

[nicolasstucki]

No description provided.

[nicolasstucki]

@biboudis do not forget to review this PR.

[biboudis]

I think it is ok related to this.

What do you think about the following? Should I open a separate issue?

import scala.quoted._

object Test{
  class Foo {
    def a: Expr[Foo] = '(new Foo) // OK
  }

  class Outer {
    class Inner{
      def b: Expr[Inner] = '(new Inner) // error: access to Outer.this from wrong staging level
    }
  }
}