Run clang-tidy modernize-use-override to remove all the redundant
virtual keywords from overridden methods, and add some missing
overrides.
Another benefit is that this has also added the overrides
on destructors, which will cause a build failure if a base
class is missing a virtual destructor.
Tools can now indicate (via setFlags()) if they desire snapping
to be active for the tool. When a tool has the flag set,
any QgsLayoutViewMouseEvents it receives will have a snappedPoint()
available which returns the mouse event point snapped using
the layout's snapping settings.
Copy the same model as QgsMapCanvas uses, with separate
classes for individual interaction tools instead of keeping
all the logic in the QGraphicsView subclass (as is done
with composer)
