macOS native:

- removed `FlatNativeMacLibrary.getWindowPtr()` because it is too dangerous to use `windowPtr` (which is `NSWindow*`) in Java (using invalid window pointer would crash app)
- made `getNSWindow()` 20x faster
- catch exceptions in `getNSWindow()`
- digitally signed dylibs

flatlaf-natives/flatlaf-natives-macos/src/main/objcpp/JNIUtils.mm

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2023 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#import <stdlib.h>
+#import "JNIUtils.h"
+
+/**
+ * @author Karl Tauber
+ */
+
+jfieldID getFieldID( JNIEnv *env, const char* className, const char* fieldName, const char* fieldSignature ) {
+//	NSLog( @"getFieldID %s %s %s", className, fieldName, fieldSignature );
+
+	jclass cls = env->FindClass( className );
+	if( cls == NULL ) {
+		NSLog( @"FlatLaf: failed to lookup class '%s'", className );
+		env->ExceptionDescribe(); // print stack trace
+		env->ExceptionClear();
+		return NULL;
+	}
+
+	jfieldID fieldID = env->GetFieldID( cls, fieldName, fieldSignature );
+	if( fieldID == NULL ) {
+		NSLog( @"FlatLaf: failed to lookup field '%s' of type '%s' in class '%s'", fieldName, fieldSignature, className );
+		env->ExceptionDescribe(); // print stack trace
+		env->ExceptionClear();
+		return NULL;
+	}
+
+	return fieldID;
+}