feat: sync fast forward volume

Adds a feature in which changing the value of the standard volume slider also changes the value of the fast forward slider.

- Tested both in global settings and in game-specific settings
- Adjustments on the fast-forward volume slider stay independent

Author: BarretoJuan

pcsx2-qt/Settings/AudioSettingsWidget.cpp

@@ -86,6 +86,7 @@ AudioSettingsWidget::AudioSettingsWidget(SettingsWindow* settings_dialog, QWidge
 		SettingWidgetBinder::BindWidgetAndLabelToIntSetting(sif, m_ui.standardVolume, m_ui.standardVolumeLabel, tr("%"), "SPU2/Output", "StandardVolume", 100);
 		SettingWidgetBinder::BindWidgetAndLabelToIntSetting(sif, m_ui.fastForwardVolume, m_ui.fastForwardVolumeLabel, tr("%"), "SPU2/Output", "FastForwardVolume", 100);
 		SettingWidgetBinder::BindWidgetToBoolSetting(sif, m_ui.muted, "SPU2/Output", "OutputMuted", false);
+		connect(m_ui.standardVolume, &QSlider::valueChanged, m_ui.fastForwardVolume, &QSlider::setValue);
 	}
 	connect(m_ui.resetStandardVolume, &QToolButton::clicked, this, [this]() { resetVolume(false); });
 	connect(m_ui.resetFastForwardVolume, &QToolButton::clicked, this, [this]() { resetVolume(true); });
@@ -308,6 +309,9 @@ void AudioSettingsWidget::onStandardVolumeChanged(const int new_value)
 	// only called for base settings
 	pxAssert(!dialog()->isPerGameSettings());
 	Host::SetBaseIntSettingValue("SPU2/Output", "StandardVolume", new_value);
+	QSignalBlocker sb(m_ui.fastForwardVolume);
+	m_ui.fastForwardVolume->setValue(new_value);
+	Host::SetBaseIntSettingValue("SPU2/Output", "FastForwardVolume", new_value);
 	Host::CommitBaseSettingChanges();
 	g_emu_thread->applySettings();