Exclude Qt6 from IMAGEVIEW_DIRECTUPDATE and IMAGEVIEW_QUICKUPDATE

Qt6, like Qt5, requires all painting to go through the standard event
loop via paintEvent(). The IMAGEVIEW_DIRECTUPDATE and IMAGEVIEW_QUICKUPDATE
optimizations bypass this, causing sluggish rendering and UI glitches
when editing or zooming.

The original code excluded Qt5 but not Qt6, which was added to Lazarus
after this code was written (2020).

Qt documentation confirms Qt6 maintains the same paint model as Qt5,
with repaint() being deprecated in favor of update() for event-driven
painting.

Author: Cordtus

lazpaint/uimageview.pas

@@ -2,9 +2,9 @@
 unit UImageView;
 
 {$mode objfpc}{$H+}
-{$IF defined(LINUX) and not defined(LCLqt5)}{$DEFINE IMAGEVIEW_DIRECTUPDATE}{$ENDIF}
+{$IF defined(LINUX) and not defined(LCLqt5) and not defined(LCLqt6)}{$DEFINE IMAGEVIEW_DIRECTUPDATE}{$ENDIF}
 {$DEFINE DRAW_TOOL_OUTSIDE_IMAGE}
-{$IF not defined(DARWIN) and not defined(LCLqt5)}{$DEFINE IMAGEVIEW_QUICKUPDATE}{$ENDIF}
+{$IF not defined(DARWIN) and not defined(LCLqt5) and not defined(LCLqt6)}{$DEFINE IMAGEVIEW_QUICKUPDATE}{$ENDIF}
 
 interface