API changes:
* (breaking) the `rotate` method is gone
* the `adjustRotation`, `adjustResolution` and `adjustZoom` methods are now
available and allow using an anchor.
This means interactions do not have to do the anchor computation themselves
and this also fix anchor computation when constraints must be applied.
This introduces a breaking change.
This options replaces the various `constrainResolution` options on interactions
and the `fit` method.
Since constraints are now the responsibility of the View, the fact that intermediary
zoom levels are allowed or not is now set in the view options.
By default, the view resolution is unconstrained.
This is done by applying the center constraint differently when we're in the
middle of an interaction/animation or not.
When the view is moving, the center constraint will restrain the given value
in an "elastic" way, using a logarithmic function.
This can be disabled using the `smoothCenterConstrain` view parameter.
This commit aims to simplify the computation of zoom and resolution in the
View class.
Previously zoom levels and resolution computations were mixed in different places,
ie resolution constraints, initial values, etc.
Now the View class only has the `getZoomForResolution` and `getResolutionForZoom`
methods to convert from one system to another.
Other than that, most computations use the resolution system internally.
The `constrainResolution` method also does not exist anymore, and is replaced
by `getValidResolution` and `getValidZoomLevel` public methods.
This introduces a breaking change:
The `extent` view option now constrains the whole viewport and not just the
view center.
The option `constrainOnlyCenter` was added to keep the previous behaviour.
Constraining the whole viewport and not only the view center means
that the center and resolution constraints must be applied with a knowledge of
the viewport size.
The `getValidZoomLevel` apply the current resolution constraint to return
a value that is guaranteed valid.
This is used for interactions & controls which need a target value to work:
the +/- buttons, the zoom clider, the dragbox zoom and the mouse wheel zoom.
