feat(layer-control): support collapsed groups and initial selection from layer visibility

[PZahnen]

Requested by XLeitstelle: the LayerControl's initial state can now be controlled from the configuration and the style.

• Groups can start collapsed: groups and radio-groups accept a new option opened (default true). With opened: false the group is collapsed when the map is loaded.
• Initial selection follows the style: instead of activating every layer on load, the LayerControl now respects the visibility layout property of the style's layers (the same value that is toggled on click):
  • layers with "visibility": "none" start unchecked and stay hidden
  • groups start checked if all of their entries are checked
  • merge-groups start checked as soon as one of their layers is visible (they are switched as a whole)
  • radio-groups select their first entry that is not hidden (falling back to the first entry)

New Storybook stories Initial State and Initial State Interactions cover this.

Follow-up in ldproxy

After this is released (changeset: minor, 1.2.0):

• bump @xtramaps/layer-control-maplibre and @xtramaps/layer-control-maplibre-react to ^1.2.0 in ogcapi-html
• add the matching documentation, already prepared in the ldproxy branch layer-control-initial-state (commit "styles: document initial state of the layer control (opened, visibility)")