Imports clauses in collective extensions

[nicolasstucki]

The idea is to allow imports in the extension clause to allow local imports that are used in all the extension methods

trait X:
  type Y

extension (x: X)
  import x.*
  def foo: Y = ??? 

Real-world example

import scala.quoted.*

extension (using Quotes)(expr: Expr[Any])
  def reflectTpe: quotes.reflect.TypeRepr =
    import quotes.reflect.*
    expr.asTerm.tpe

  def reflectPos: quotes.reflect.Position =
    import quotes.reflect.*
    expr.asTerm.pos

would become

import scala.quoted.*

extension (using Quotes)(expr: Expr[Any])
  import quotes.reflect.*
  def reflectTpe: TypeRepr = expr.asTerm.tpe
  def reflectPos: Position = expr.asTerm.pos