UI: Show "stopping" text on buttons when waiting for stop

The new cutoff timing fix means that streaming/recording has to remain
active for bit until the stream/recording has reached the expecting stop
timestamp.  This means that the buttons would continue to say "Stop
streaming/recording" while waiting for the output to stop itself at the
appropriate timing.

So instead of letting it do that and confusing the user, the buttons
will now say "stopping" when the button is pressed to indicate to the
user that the stream/recording is in the process of stopping.

obs/window-basic-main.cpp

@@ -3422,6 +3422,11 @@ void OBSBasic::StreamingStart()
 	blog(LOG_INFO, STREAMING_START);
 }
 
+void OBSBasic::StreamStopping()
+{
+	ui->streamButton->setText(QTStr("Basic.Main.StoppingStreaming"));
+}
+
 void OBSBasic::StreamingStop(int code)
 {
 	const char *errorMessage;
@@ -3482,6 +3487,11 @@ void OBSBasic::StartRecording()
 		outputHandler->StartRecording();
 }
 
+void OBSBasic::RecordStopping()
+{
+	ui->recordButton->setText(QTStr("Basic.Main.StoppingRecording"));
+}
+
 void OBSBasic::StopRecording()
 {
 	SaveProject();