False positive exhaustivity warnings for a custom tuple class

[dwijnand]

Continuation of #10373, but for custom tuple classes.

Using Scala 2.13.3

abstract class Foo {
    def bar(): Unit = this match {
        case Foo_1() => //do something
        case Foo_2() => //do something
        // emits no warning
    }
    
    def blitz(that: Foo): Unit = T2(this, that) match {
        case T2(Foo_1(), _) => //do something
        case T2(Foo_2(), _) => //do something
        // emits "match may not be exhaustive"
    }
}
case class Foo_1() extends Foo
case class Foo_2() extends Foo

final case class T2[A, B](a: A, b: B)

Some analysis notes at scala/scala#9163 (comment).