Rename Reflection.Type to TypeRepr

[nicolasstucki]

Renaming this will fix all ambiguities between quoted.Type and reflect.Type that are imported in the same scope.
This happened every time we imported reflection. For example in

import scala.quoted._ // import scala.quoted.Type
def f(using QuoteContext): Expr[Unit] = {
  import qctx.reflect._ // used to shadow scala.quoted.Type with qctx.reflect.Type
  def f[T:Type] = ... // error
  ...
}

After this change, the code above works.

[liufengyun]

LGTM

Minor: TypeRep vs TypeRepr, I find the former shorter, but not a big deal.