[K/N] Migrate some cinterop tests to new test infra

native/native.tests/testData/CInterop/executable/toKString/toKString.def

@@ -0,0 +1,6 @@
+---
+const char* empty() { return ""; }
+const char* foo() { return "foo"; }
+const char* kuku() { return "куку"; }
+const char* invalid_utf8() { return "\x85\xAF"; }
+const char* zero_in_the_middle() { return "before zero\0after zero"; }

native/native.tests/testData/CInterop/executable/toKString/toKString.kt

@@ -0,0 +1,14 @@
+@file:OptIn(kotlinx.cinterop.ExperimentalForeignApi::class)
+
+import toKString.*
+import kotlinx.cinterop.*
+import kotlin.native.*
+import kotlin.test.*
+
+fun main() {
+    assertEquals("", empty()!!.toKStringFromUtf8())
+    assertEquals("foo", foo()!!.toKStringFromUtf8())
+    assertEquals("куку", kuku()!!.toKStringFromUtf8())
+    assertEquals("\uFFFD\uFFFD", invalid_utf8()!!.toKStringFromUtf8())
+    assertEquals("before zero", zero_in_the_middle()!!.toKStringFromUtf8())
+}