Refutable extractor may be an Apply tree

[griggt]

Fixes #15650

[dwijnand]

Let's avoid MatchErrors outright, by using the recursive funPart, and falling back if it's not a select.

[dwijnand]

Suggested change

	fn match
	case Select(id, _) => id
	case Apply(Select(id, _), _) => id
	case TypeApply(Select(id, _), _) => id
	em"pattern binding uses refutable extractor `$extractor`"
	tpd.funPart(fn) match
	case Select(id, _) => id
	case _ => ""
	if extractor == ""
	em"pattern binding uses refutable extractor"
	else
	em"pattern binding uses refutable extractor `$extractor`"

[griggt]

oooh, was unaware of funPart, very nice, thanks!

[bishabosha]

extracting the extractor name needs to deal with arbitrary parameter lists (and type parameter lists for future proofing), for example it still crashes if I add another using clause:

class Rational

import scala.quoted.*

class TC

object meta:
  object rationalTE:
    def unapply(using Quotes)(using TC)(tr: quotes.reflect.TypeRepr): Option[Rational] = ???

  def foo(using Quotes)(using TC)(p: quotes.reflect.TypeRepr): Unit =
    val rationalTE(e) = p  // warn: pattern binding uses refutable extractor `meta.rationalTE`

[dwijnand]

Yeah, using TreeInfo's funPart will address that.

[griggt]

Rebased with suggested changes and an additional test case.