Instantiate QCoreTextFontDatabaseEngineFactory, not just base class

We were instantiating the QCoreTextFontDatabase base class, which
doesn't provide the full set of required functions.

Task-number: QTBUG-65078
Change-Id: I4dbe50b594ca25c61f748170acf29fcaabc65c0b
Reviewed-by: Tor Arne Vestbø <[email protected]>

Author: jsfdez

src/plugins/platforms/webgl/qwebglintegration_p.h

@@ -43,6 +43,7 @@
 #include <QtFontDatabaseSupport/private/qwindowsfontdatabase_p.h>
 #include <QtEventDispatcherSupport/private/qwindowsguieventdispatcher_p.h>
 #elif defined(Q_OS_MACOS)
+#include <QtFontDatabaseSupport/private/qfontengine_coretext_p.h>
 #include <QtFontDatabaseSupport/private/qcoretextfontdatabase_p.h>
 #include <QtEventDispatcherSupport/private/qgenericunixeventdispatcher_p.h>
 #else
@@ -73,7 +74,7 @@ class QWebGLIntegrationPrivate
 #if defined(Q_OS_WIN)
     mutable QWindowsFontDatabase fontDatabase;
 #elif defined(Q_OS_MACOS)
-    mutable QCoreTextFontDatabase fontDatabase;
+    mutable QCoreTextFontDatabaseEngineFactory<QCoreTextFontEngine> fontDatabase;
 #else
     mutable QGenericUnixFontDatabase fontDatabase;
 #endif