Remember the last center position in the map view

[abey79]

What

When ever we compute a center position from the data, we keep it around in the view state such that we can use it should the data suddenly disappear (aka. time cursor to before data was born, or empty range visible history).

Part of:

• Buggy maps view with time range #8109

map_remember_center_position.mp4

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[Wumpf]

delightful!