qtglrenderer.cc: Add missing QCoreApplication and QEventLoop includes

This fixes a build error if Qt was build without accessibility support:

../../../../../gstreamer/subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc:
    In member function 'bool GstQuickRenderer::init(GstGLContext*, GError**)':
../../../../../gstreamer/subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc:341:13:
    error: 'QCoreApplication' was not declared in this scope; did you mean 'QApplication'?
../../../../../gstreamer/subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc:341:31:
    error: 'app' was not declared in this scope
../../../../../gstreamer/subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc:341:37:
    error: 'QCoreApplication' is not a class, namespace, or enumeration
[...]
../../../../../gstreamer/subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc:458:5:
    error: 'QEventLoop' was not declared in this scope; did you mean 'QEvent'?
../../../../../gstreamer/subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc:459:9:
    error: 'loop' was not declared in this scope

If accessibility is enabled, the includes for QCoreApplication and QEventLoop
are indirectly pulled via QWidget.

Add the required headers as documented in [1] and [2].

[1] https://doc.qt.io/qt-5/qcoreapplication.html
[2] https://doc.qt.io/qt-5/qeventloop.html

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4815>

subprojects/gst-plugins-good/ext/qt/qtglrenderer.cc

@@ -9,6 +9,8 @@
 #include <QOpenGLFunctions>
 #include <QOpenGLFramebufferObject>
 #include <QAnimationDriver>
+#include <QCoreApplication>
+#include <QEventLoop>
 
 #include <gst/gl/gl.h>
 #include "gstqtgl.h"

subprojects/gst-plugins-good/ext/qt6/qt6glrenderer.cc

@@ -10,6 +10,8 @@
 #include <QOpenGLContext>
 #include <QOpenGLFunctions>
 #include <QAnimationDriver>
+#include <QCoreApplication>
+#include <QEventLoop>
 
 #include <gst/gl/gl.h>
 #include "gstqt6gl.h"