Prevent jittering pixels using FullViewportUpdate

In the canvas view. The default MinimalViewportUpdate has some
inaccuracies that cause pixels to jitter in changed areas at certain
zooms and/or rotations. Updating the whole view instead is stable.

This was contributed by Meru.

ChangeLog

@@ -48,6 +48,7 @@ Unreleased Version 2.2.0-pre
  * Fix: Don't act like keep aspect ratio is checked when resizing from a selection. Thanks Meru for reporting.
  * Fix: Make onion skin color partially transparent by default so that they don't turn into solid blocks on colored stuff. Thanks BulletPepper for reporting.
  * Fix: Clarify the host dialog by adding additional messages that explain common sources of confusion, such as the title being required, the password being necessary to host a private session and "host on this computer" requiring port forwarding.
+ * Fix: Prevent jittering pixels on the canvas at certain zooms and rotations. Thanks Bluestrings, Meru and taiyu for reporting this. Also thanks Meru for actually finding the solution and contributing this fix.
 
 2023-11-12 Version 2.2.0-beta.10
  * Fix: Don't deadlock on first startup. Thanks to Hail, lowontrash, FARBOL234, Dorokinyo and hamlin for reporting.

src/desktop/scene/canvasview.cpp

@@ -72,6 +72,7 @@ CanvasView::CanvasView(QWidget *parent)
 	, m_blockNotices{false}
 	, m_hoveringOverHud{false}
 {
+	setViewportUpdateMode(FullViewportUpdate);
 	viewport()->setAcceptDrops(true);
 	viewport()->setAttribute(Qt::WA_AcceptTouchEvents);
 	viewport()->setMouseTracking(true);