macOS: Add missing QT_MANGLE_NAMESPACE

KeyValueObserver and RunLoopModeTracker were causing
“Class is implemented in both...” messages when loading
multiple namespaced Qt versions into the same process.

Change-Id: Idbd2229c61cde6fba2c12b35d045390a371dee68
Fixes: QTBUG-89059
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit c2c163a7d8cb95a4901b742a72184975e791635a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qcore_mac.mm

@@ -526,7 +526,7 @@ void QMacKeyValueObserver::removeObserver() {
 KeyValueObserver *QMacKeyValueObserver::observer = [[KeyValueObserver alloc] init];
 
 QT_END_NAMESPACE
-@implementation KeyValueObserver
+@implementation QT_MANGLE_NAMESPACE(KeyValueObserver)
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
         change:(NSDictionary<NSKeyValueChangeKey, id> *)change context:(void *)context
 {

src/corelib/kernel/qeventdispatcher_cf.mm

@@ -89,7 +89,7 @@ QT_USE_NAMESPACE
 
 QT_NAMESPACE_ALIAS_OBJC_CLASS(RunLoopModeTracker);
 
-@implementation RunLoopModeTracker {
+@implementation QT_MANGLE_NAMESPACE(RunLoopModeTracker) {
     QStack<CFStringRef> m_runLoopModes;
 }