Avoid regexp not supported in old browsers

Avoid regexp not supported in old browsers

This comes after a user reported that the slippy map doesn't work on iOS 15,
which we have been able to reproduce with an old iPhone.

MapLibre's translation string keys are in CapitalisedCamelCase, as opposed to
our usual snake_case. This also conflicts with Leaflet's keys which are
also in snake_case. This creates a weird scenario where a translation key
is duplicated: `GeolocateControl` for MapLibre and `geolocate_control` for
leaflet.

The original translation strings can be seen at:
- https://github.com/maplibre/maplibre-gl-js/blob/8ebe6a085e934f1b136ead624a92abdf6399f7e2/src/ui/default_locale.ts
- https://github.com/domoritz/leaflet-locatecontrol/blob/a122fb1bfe1ad39d20382e1545eaa8cb367c48fd/src/L.Control.Locate.js