[map] Support buffer for zoom geometries

[mbeckem]

Issue description

mapModel.zoom (and highlightAndZoom) should support a buffer parameter.

If the zoom geometry resolves to an extent (not a point), then that extent should be grown by the given buffer.
This is a quick and easy way to leave a certain amount of free space in all directions (e.g. 10%).

Links:

• ol/extent (function buffer): https://openlayers.org/en/latest/apidoc/module-ol_extent.html
• Highlights.ts, where the extent needs to be modified: https://github.com/open-pioneer/trails-openlayers-base-packages/blob/16a9887e0edf37f3236ed52f9a63c9cea186e0ea/src/packages/map/model/Highlights.ts#L141C1-L147C47

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