First, this function calculates the zoom out effect until both the
current Map center and the target rectangle are visible - see the
"calculate zoom out" part.
Then it calculates a zoom level, so that the target rectangle
fits the viewport, but also so that the zoom is not too much (clamped).
see the "calculate zoom in" part.
NOTE: "centerStored" (the variable used to store the current map center)
is created using QtPositioning.coordinate(), because the code needs a new
object and not a reference of the map.center QGeoCoordinate object.
Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
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