feat: add handling of lat, lon coordinate queries (#368)

Quick, *pure js* implementation to handle coordinate queries (#147). If
a user enters valid coordinates, they get a single result with that
point (as in Google Maps and other services). It's a useful feature for
power users.

![image](https://github.com/smeijer/leaflet-geosearch/assets/8945883/775ac7a2-3802-44e8-a3d5-c59d91d579e6)

Any other queries are sent to the Provider. Happy to see this in
TypeScript and otherwise improved, it's probably not ready for merging.

---------

Co-authored-by: Stephan Meijer <stephan.meijer@gmail.com>

src/SearchControl.ts

@@ -3,6 +3,7 @@ import { ControlPosition, FeatureGroup, MarkerOptions, Map } from 'leaflet';
 import SearchElement from './SearchElement';
 import ResultList from './resultList';
 import debounce from './lib/debounce';
+import { validateCoords } from './coords';
 
 import {
   createElement,
@@ -373,7 +374,13 @@ const Control: SearchControl = {
     const { provider } = this.options;
 
     if (query.length) {
-      let results = await provider!.search({ query });
+      let results = [];
+      const coords = validateCoords(query);
+      if (coords) {
+        results = coords;
+      } else {
+        results = await provider!.search({ query });
+      }
       results = results.slice(0, this.options.maxSuggestions);
       this.resultList.render(results, this.options.resultFormat);
     } else {
@@ -385,7 +392,13 @@ const Control: SearchControl = {
     this.resultList.clear();
     const { provider } = this.options;
 
-    const results = await provider!.search(query);
+    let results = [];
+    const coords = validateCoords(query);
+    if (coords) {
+      results = coords;
+    } else {
+      results = await provider!.search(query);
+    }
 
     if (results && results.length > 0) {
       this.showResult(results[0], query);

src/coords.ts

@@ -0,0 +1,23 @@
+// @ts-nocheck
+
+export function validateCoords(query) {
+  const q = query.trim();
+  const regex = /^(-?[0-9]*\.?\s*[0-9]*)\s*,?\s*(-?[0-9]*\.?[0-9]*)$/g;
+  const match = regex.exec(q);
+  if (match) {
+    const lat = Number(match[1]);
+    const lng = Number(match[2]);
+    if (-90 < lat < 90 && -180 < lng < 180) {
+      return [
+        {
+          x: lng,
+          y: lat,
+          label: q,
+          bounds: null,
+          raw: {},
+        },
+      ];
+    }
+  }
+  return false;
+}