[K2/N] Export C adapters for non-root packages

^KT-56182

Merge-request: KT-MR-10160
Merged-by: Vladimir Sukharev <Vladimir.Sukharev@jetbrains.com>

kotlin-native/backend.native/tests/interop/kt56182_subpackage2lvl/test.cpp

@@ -0,0 +1,28 @@
+#include "testlib_api.h"
+
+#include <thread>
+
+int main() {
+    auto t = std::thread([] {
+        auto lib = testlib_symbols();
+
+        lib->kotlin.root.knlibrary.subpackage.enableMemoryChecker();
+
+        // Initialize A and B.Companion and get their stable pointers.
+        auto a = lib->kotlin.root.knlibrary.subpackage.A._instance();
+        auto bCompanion = lib->kotlin.root.knlibrary.subpackage.B.Companion._instance();
+
+        // Now, dispose of the stable pointers.
+        lib->DisposeStablePointer(bCompanion.pinned);
+        lib->DisposeStablePointer(a.pinned);
+
+        // A and B.Companion now are owned by the global references only.
+    });
+
+    // This causes Kotlin runtime full deinitialization, because `t` is the only thread
+    // with the Kotlin runtime. So, all the globals will get deinitialized and memory
+    // leak checker will get executed (because .kt code is compiled with -g).
+    t.join();
+
+    return 0;
+}