Test: ~Copyable passed inout within closure

Add test coverage for a code pattern that briefly broke on main.

rdar://162749287

Author: kavon

test/SILOptimizer/moveonly_correct.swift

@@ -23,4 +23,17 @@ public struct M_109232806: ~Copyable {
 }
 public func test_109232806(m: borrowing M_109232806) {
   _ = m.y
+}
+
+
+// rdar://162749287
+struct DonutEventHandler: ~Copyable {
+    mutating func deliciouslyDo<Result>(
+        operation: (inout Self) async throws -> Result,
+        withHandler handler: (Int) async throws -> Void
+    ) async rethrows -> Result {
+        return try await withoutActuallyEscaping(handler) { escapingHandler in
+            return try await operation(&self)
+        }
+    }
 }