UI: Make settings -> 'Audio' source list expand vertically

Reduces required scrolling when lots of new audio sources are added
(e.g. aux devices being enabled in the same dialog) when the dialog
was opened with just a few audio sources being present. Unfortunately,
the "restart required" warning is pushed all the way to the bottom
even if the source list is empty

obs/window-basic-settings.cpp

@@ -222,6 +222,10 @@ OBSBasicSettings::OBSBasicSettings(QWidget *parent)
 
 	ui->listWidget->setAttribute(Qt::WA_MacShowFocusRect, false);
 
+	auto policy = ui->audioSourceScrollArea->sizePolicy();
+	policy.setVerticalStretch(true);
+	ui->audioSourceScrollArea->setSizePolicy(policy);
+
 	HookWidget(ui->language,             COMBO_CHANGED,  GENERAL_CHANGED);
 	HookWidget(ui->theme, 		     COMBO_CHANGED,  GENERAL_CHANGED);
 	HookWidget(ui->outputMode,           COMBO_CHANGED,  OUTPUTS_CHANGED);