Refutable extractor may be an Apply tree

Fixes #15650

Author: griggt

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -832,6 +832,7 @@ trait Checking {
             val UnApply(fn, _, _) = pat: @unchecked
             fn match
               case Select(id, _) => id
+              case Apply(Select(id, _), _) => id
               case TypeApply(Select(id, _), _) => id
           em"pattern binding uses refutable extractor `$extractor`"
 

tests/pos/i15650.scala

@@ -0,0 +1,10 @@
+class Rational
+
+import scala.quoted.*
+
+object meta:
+  object rationalTE:
+    def unapply(using Quotes)(tr: quotes.reflect.TypeRepr): Option[Rational] = ???
+
+  def foo(using Quotes)(p: quotes.reflect.TypeRepr): Unit =
+    val rationalTE(e) = p  // warn: pattern binding uses refutable extractor `meta.rationalTE`