Change example "measure" from using in to something else

[tordans]

The https://maplibre.org/maplibre-gl-js/docs/examples/measure/ example is referenced in https://maplibre.org/maplibre-style-spec/expressions/#in as a good way to learn how in works.

However, the code it shows filter: ['in', '$type', 'Point'] does not represent a good case for in. It is a simple "match" condition, not an array lookup nor a substring match.

Can we change this example to using ["all", ["match", ["geometry-type"], ["Polygon"], true, false]] or ["all", "$type", ["Polygon"], true, false]] or ["==", "$type", "Polygon"] or something like this?

See also #664

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This would mean we don't have an in example anymore (which I would argue we don't have now, either). I would consider something like https://visgl.github.io/react-map-gl/examples/filter (Code) a better fit. But even better would be a case with a ['literal', ['array']] IMO.