Fix adjusting selection geometry when exporting from gui

The docs for `setTopLeft()` say

    "Set the top-left corner of the rectangle to the given position. May
    change the size, but will never change the bottom-right corner of
    the rectangle."

For some reason on windows when calling `setTopLeft()` here when the
widget is at an offset it is moving the top left of the rect but not
keeping the size the same. I believe all we want to do here is move the
rect, so this commit changes this adjustment to definitively do that.
There are various instances of `move()`, `moveTo()` and `moveTopLeft()`
in the codebase, and only one other if `setTopLeft()`. I picked
`moveTopLeft()` because it makes the diff smaller ;)

This error has the following implications 1) causing the pin widget
to shift a little from where the selection was 2) causing the reported
geometry to not match the pixmap size, which didn't have much effect
unless you wanted to use the geometry later (for example for allowing
editing pins). I guess the pin widget got its size from the pixmap or
something and that's why it wasn't huge?

You can reproduce this like so:

* have a windows machine with two monitors
* change the display settings so monitor one is to the right of monitor
  two (which causes monitor two to have a negative offset)
* pin a selection and watch the pinned window shift a bit from where the
  selection was; or
* observe this modified geometry somehow, like this patch which changes
  the size measurement painted on the selection widget to include the
  modified geometry alongside the original one:

    diff --git c/src/widgets/capture/capturewidget.cpp w/src/widgets/capture/capturewidget.cpp
    index 49ebff9720a0..16c7d04dbed6 100644
    --- c/src/widgets/capture/capturewidget.cpp
    +++ w/src/widgets/capture/capturewidget.cpp
    @@ -551,11 +633,18 @@ void CaptureWidget::paintEvent(QPaintEvent* paintEvent)
             QRect xybox;
             QFontMetrics fm = painter.fontMetrics();

    -        QString xy = QString("%1x%2+%3+%4")
    +        QRect final_geometry(m_context.selection);
    +        final_geometry.setTopLeft(final_geometry.topLeft() + m_context.widgetOffset);
    +        QString xy = QString("%1x%2+%3+%4\n%5x%6+%7+%8")
                            .arg(static_cast<int>(selection.width() * scale))
                            .arg(static_cast<int>(selection.height() * scale))
                            .arg(static_cast<int>(selection.left() * scale))
    -                       .arg(static_cast<int>(selection.top() * scale));
    +                       .arg(static_cast<int>(selection.top() * scale))
    +                       .arg(static_cast<int>(final_geometry.width() * scale))
    +                       .arg(static_cast<int>(final_geometry.height() * scale))
    +                       .arg(static_cast<int>(final_geometry.left() * scale))
    +                       .arg(static_cast<int>(final_geometry.top() * scale))
    +                       ;

             xybox = fm.boundingRect(xy);
             // the small numbers here are just margins so the text doesn't

https://doc.qt.io/qt-6/qrect.html#setTopLeft

src/widgets/capture/capturewidget.cpp

@@ -200,7 +200,7 @@ CaptureWidget::~CaptureWidget()
         auto lastRegion = m_selection->geometry();
         setLastRegion(lastRegion);
         QRect geometry(m_context.selection);
-        geometry.setTopLeft(geometry.topLeft() + m_context.widgetOffset);
+        geometry.moveTopLeft(geometry.topLeft() + m_context.widgetOffset);
         Flameshot::instance()->exportCapture(
           pixmap(), geometry, m_context.request);
     } else {