fix: remove javapart ref from cpp nativeproxy (#2934)

PR analogous to software-mansion/react-native-reanimated#7515 regarding the `javaPart_`. 
Right now when you do a reload in a simple app with screens installed, you will see in AS profiler that instances of all NativeProxys are still in the memory. It is caused by `javaPart_` never being released thus keeping java part after reload.

I also removed empty destructor of `NativeProxy`.

Author: WoLewicki

android/src/fabric/java/com/swmansion/rnscreens/NativeProxy.kt

@@ -20,6 +20,8 @@ class NativeProxy {
 
     external fun nativeAddMutationsListener(fabricUIManager: FabricUIManager)
 
+    external fun invalidateNative()
+
     companion object {
         // we use ConcurrentHashMap here since it will be read on the JS thread,
         // and written to on the UI thread.

android/src/main/cpp/NativeProxy.cpp

@@ -14,14 +14,13 @@ namespace rnscreens {
 NativeProxy::NativeProxy(jni::alias_ref<NativeProxy::javaobject> jThis)
     : javaPart_(jni::make_global(jThis)) {}
 
-NativeProxy::~NativeProxy() {}
-
 void NativeProxy::registerNatives() {
   registerHybrid(
       {makeNativeMethod("initHybrid", NativeProxy::initHybrid),
        makeNativeMethod(
            "nativeAddMutationsListener",
-           NativeProxy::nativeAddMutationsListener)});
+           NativeProxy::nativeAddMutationsListener),
+       makeNativeMethod("invalidateNative", NativeProxy::invalidateNative)});
 }
 
 void NativeProxy::nativeAddMutationsListener(
@@ -48,4 +47,8 @@ jni::local_ref<NativeProxy::jhybriddata> NativeProxy::initHybrid(
   return makeCxxInstance(jThis);
 }
 
+void NativeProxy::invalidateNative() {
+    javaPart_ = nullptr;
+}
+
 } // namespace rnscreens

android/src/main/cpp/NativeProxy.h

@@ -19,8 +19,6 @@ class NativeProxy : public jni::HybridClass<NativeProxy> {
       jni::alias_ref<jhybridobject> jThis);
   static void registerNatives();
 
-  ~NativeProxy();
-
  private:
   friend HybridBase;
   jni::global_ref<NativeProxy::javaobject> javaPart_;
@@ -30,6 +28,8 @@ class NativeProxy : public jni::HybridClass<NativeProxy> {
   void nativeAddMutationsListener(
       jni::alias_ref<facebook::react::JFabricUIManager::javaobject>
           fabricUIManager);
+
+  void invalidateNative();
 };
 
 } // namespace rnscreens

android/src/main/java/com/swmansion/rnscreens/ScreensModule.kt

@@ -39,6 +39,7 @@ class ScreensModule(
 
     override fun invalidate() {
         super.invalidate()
+        proxy?.invalidateNative();
         nativeUninstall()
     }
 

android/src/paper/java/com/swmansion/rnscreens/NativeProxy.kt

@@ -6,6 +6,8 @@ class NativeProxy {
     // do nothing on Paper
     fun nativeAddMutationsListener(fabricUIManager: FabricUIManager) = Unit
 
+    fun invalidateNative() = Unit
+
     companion object {
         fun addScreenToMap(
             tag: Int,