macosx: slow down the forward/backward buttons a bit (close #6135)

continous button action skips 1 minute within 5 secs now, which matches iTunes

note that iTunes gets faster if you press the button longer, which is something we might want to do as well
(cherry picked from commit 86572c9fec46e3f4ea530e0ed1f0471eed66c735)

modules/gui/macosx/MainWindow.m

@@ -524,10 +524,10 @@ static VLCMainWindow *_o_sharedInstance = nil;
     }
     else
     {
-        if (([NSDate timeIntervalSinceReferenceDate] - last_fwd_event) > 0.12 )
+        if (([NSDate timeIntervalSinceReferenceDate] - last_fwd_event) > 0.16 )
         {
-            // we just skipped 3 "continous" events, otherwise we are too fast
-            [[VLCCoreInteraction sharedInstance] backward];
+            // we just skipped 4 "continous" events, otherwise we are too fast
+            [[VLCCoreInteraction sharedInstance] backwardExtraShort];
             last_bwd_event = [NSDate timeIntervalSinceReferenceDate];
             [self performSelector:@selector(resetBackwardSkip)
                        withObject: NULL
@@ -563,10 +563,10 @@ static VLCMainWindow *_o_sharedInstance = nil;
     }
     else
     {
-        if (([NSDate timeIntervalSinceReferenceDate] - last_fwd_event) > 0.12 )
+        if (([NSDate timeIntervalSinceReferenceDate] - last_fwd_event) > 0.16 )
         {
-            // we just skipped 3 "continous" events, otherwise we are too fast
-            [[VLCCoreInteraction sharedInstance] forward];
+            // we just skipped 4 "continous" events, otherwise we are too fast
+            [[VLCCoreInteraction sharedInstance] forwardExtraShort];
             last_fwd_event = [NSDate timeIntervalSinceReferenceDate];
             [self performSelector:@selector(resetForwardSkip)
                        withObject: NULL