add install addon functionality

packages/flutter_mozilla_components/android/src/main/kotlin/eu/lensai/flutter_mozilla_components/api/GeckoAddonsApiImpl.kt

@@ -24,4 +24,16 @@ class GeckoAddonsApiImpl(private val context: Context) : GeckoAddonsApi {
             WebExtensionActionType.PAGE -> components.features.webExtensionToolbarFeature.invokeAddonPageAction(extensionId)
         }
     }
+
+    override fun installAddon(url: String, callback: (Result<Unit>) -> Unit) {
+        components.core.addonManager.installAddon(
+            url = url,
+            onSuccess = { _ ->
+                callback(Result.success(Unit))
+            },
+            onError = { e ->
+                callback(Result.failure(e))
+            }
+        )
+    }
 }

packages/flutter_mozilla_components/lib/src/domain/services/gecko_addon.dart

@@ -39,6 +39,10 @@ class GeckoAddonService extends GeckoAddonEvents {
     return _api.invokeAddonAction(extensionId, actionType);
   }
 
+  Future<void> installAddon(Uri url) {
+    return _api.installAddon(url.toString());
+  }
+
   @override
   void onRemoveWebExtensionAction(
     int timestamp,

packages/flutter_mozilla_components/pigeons/gecko.dart

@@ -1058,6 +1058,9 @@ abstract class GeckoAddonsApi {
   void startAddonManagerActivity();
 
   void invokeAddonAction(String extensionId, WebExtensionActionType actionType);
+
+  @async
+  void installAddon(String url);
 }
 
 @FlutterApi()