Test order-dependent reachability warnings

Author: dwijnand

tests/patmat/i13485.check

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+16: Match case Unreachable

tests/patmat/i13485.scala

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+// The intent of this test is test that changing the order of cases doesn't affect whether
+// warnings, originally reachability warnings but exhaustivity warnings too, are emitted.
+// To do so we need a case that typechecks but is statically assessed to be unreachable.
+// How about... a type pattern on a sealed trait that the scrutinee type doesn't extend?
+
+sealed trait Foo
+
+class Bar
+
+def test1(bar: Bar) = bar match
+  case _: Foo => 1
+  case _: Bar => 2
+
+def test2(bar: Bar) = bar match
+  case _: Bar => 2
+  case _: Foo => 1