Crash when pickling buggy macro implementation

[nicolasstucki]

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

Note that this code should have (x: Expr[X]) in fooImpl.

It crashes with:

Exception in thread "main" java.lang.AssertionError: assertion failed: unresolved symbols: type X when pickling Foo.scala
	at scala.Predef$.assert(Predef.scala:219)
	at dotty.tools.dotc.core.tasty.TreePickler.pickle(TreePickler.scala:639)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.pickle(PickledQuotes.scala:98)
	at dotty.tools.dotc.core.quoted.PickledQuotes$.pickleQuote(PickledQuotes.scala:31)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.pickleAsTasty$1(ReifyQuotes.scala:401)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.pickledQuote(ReifyQuotes.scala:416)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.quotation(ReifyQuotes.scala:389)
	at dotty.tools.dotc.transform.ReifyQuotes$Reifier.$anonfun$transform$2(ReifyQuotes.scala:547)
	... 

[nicolasstucki]

Possibly caused by #4493