Synthesize class tags in top level splices.

[nicolasstucki]

object Foo {
  inline def foo[X](x: X): Unit = ~fooImpl('(x))
  def fooImpl[X: quoted.Type](x: quoted.Expr[X]): quoted.Expr[Unit] = '()
}

currently fails with

3 |  inline def foo[X](x: X): Unit = ~fooImpl('(x))
  |                                                ^
  |no implicit argument of type quoted.Type[X] was found for parameter evidence$1 of method fooImpl in object Foo

We need to write instead

  inline def foo[X](x: X): Unit = ~fooImpl('(x))('[X])

We should be able to synthesize classtags inside top level splices to reduce this syntactic overhead.

This would be a change in Typer and not in ReifyQuotes.

[nicolasstucki]

We also need to make Universe.compilationUniverse available in this same scope. A solution would be to add Universe._ to the scope of a top level splice.
Converting

inline def foo[X](x: X): Unit = ~{ ... }

into

inline def foo[X](x: X): Unit = ~{ import Universe._; ... }

This must be done durring typing or before.

Then we can add implicit inline def tp[T]: scala.quoted.Type[T] = scala.quoted.Type.apply[T] to Universe to provide the type tags.