Add overpass_api_ui submodule: Overpass query builder GUI (like QuickOSM)

Problem/Motivation

The overpass_api module currently exposes Overpass API access purely as a service (OverpassApi::query() / rawQuery()). There is no interactive UI for building an Overpass QL query: any site builder who wants to fetch OSM data has to hand-write Overpass QL and call the service from custom code.

The QGIS QuickOSM plugin solves exactly this problem for QGIS users with a query-builder GUI (query type selector, key/value filters, bounding box / named-area / around-area spatial modes, raw query editor). This issue proposes a Drupal-native equivalent as a new submodule, so Drupal site builders get the same experience without leaving the browser.

Proposed resolution

Add a new submodule, overpass_api_ui, depending on overpass_api, drupal/geocoder (+ geocoder-php/nominatim-provider), and drupal/leaflet:

• A QueryBuilderForm with 5 query-type modes: NotSpatial (attribute-only), BBox, InArea, AroundArea, and a raw query editor for hand-written OQL/XML.
• Shared controls across the spatial modes: OSM type checkboxes (node/way/relation), a dynamic (AJAX add/remove) key/value filter table with AND/OR between rows.
• InArea/AroundArea resolve a free-text place name to an OSM ID / lat-lon via the geocoder service (Nominatim provider), Overpass's own {{geocodeArea:name}}/{{geocodeCoords:name}} tokens are client-side template syntax from overpass-turbo/QuickOSM, not real Overpass QL, so this resolution has to happen before the query is sent.
• BBox mode gets an interactive Leaflet map (via the Geoman drawing controls bundled with drupal/leaflet) to draw a rectangle, two-way synced with the 4 numeric lat/lon fields.
• A live, read-only "generated query" preview pane shows the actual OQL that will be submitted, post geocoder-resolution.
• Running the query calls the existing OverpassApi::rawQuery() and renders: an elements table (osm_id, osm_type, flattened tags), a raw-JSON toggle, a Leaflet map rendering the result set as a GeoJSON overlay, and a "download as .json" button.

Remaining tasks

• Scaffold overpass_api_ui.info.yml / .routing.yml / .permissions.yml / .services.yml / .libraries.yml.
• Implement the overpass_api_ui.query_builder service (form values → OQL fragment string), unit-tested independently of HTTP.
• Implement QueryBuilderForm with the 5 query-type modes and shared key/value filter table (#ajax + #states).
• Wire up geocoder/Nominatim resolution for InArea/AroundArea, including the OSM-ID → Overpass area-ID math.
• Wire up the Leaflet map: bbox rectangle drawing (BBox mode), radius-circle preview (AroundArea), GeoJSON result overlay.
• Implement results rendering: elements table, raw-JSON toggle, JSON download.
• Unit tests for the query-builder service; extend existing PHPUnit/PHPCS suites.
• User documentation for the new form.

User interface changes

New admin/user-facing route and form (e.g. /admin/config/system/overpass-api/query-builder), gated by a new permission (e.g. use overpass api ui). No changes to the existing overpass_api settings form.

The form uses a single "Query type" radios field (NotSpatial / BBox / InArea / AroundArea / Raw query) with mode-specific fieldsets shown or hidden via Drupal's #states API, rather than separate tabs per mode. Shared controls (OSM type checkboxes, key/value filter table) stay outside the conditional area so there is one AJAX-managed instance instead of duplicating it per mode.

API changes

New service: overpass_api_ui.query_builder. No changes to the existing overpass_api API surface (OverpassApi, OverpassQueryOptions). This submodule consumes them as-is.

Data model changes

None. No new entities, config schema, or database tables. Query building and result display are transient/in-request only.