Permalink: add swisssearch parameter handling

https://github.com/geoadmin/mf-geoadmin3/issues/586

This PR adds feature parity with RE2. A search is triggered on page load when the `swisssearch` parameter is present. If the search returns exactly 1 result, the result is activated (as if clicked by the user). This is the same behaviour as in RE2.

Note: this PR likely conflicts with https://github.com/geoadmin/mf-geoadmin3/pull/1345. Whichever is merged later will probably need a rebasing.

Note: To have only 1 result (and therefore re-location of map), you have to be very specific. Simply putting `Payerne` is not enough. Therefore, this is not really usable for SEO out of the box.