[Tests] Migrate backend-independent tests from native to compiler/testData.

^KT-65979

compiler/testData/codegen/box/contracts/require.kt

@@ -0,0 +1,21 @@
+// WITH_STDLIB
+import kotlin.test.*
+import kotlin.contracts.*
+
+open class S
+class P(val str: String = "P") : S()
+
+@OptIn(kotlin.contracts.ExperimentalContracts::class)
+fun check(actual: Boolean) {
+    contract { returns() implies actual }
+    assertTrue(actual)
+}
+
+fun box(): String {
+    val s: S = P()
+
+    require(s is P)
+    assertEquals(s.str, "P")
+
+    return "OK"
+}