fix(composables): use string as injection key

Because reasons

Author: brawaru

src/consts.ts

@@ -1,6 +1 @@
-import type { InjectionKey } from 'vue'
-import type { IntlController } from './controller.js'
-
-export const controllerKey = Symbol('vueIntlController') as InjectionKey<
-  IntlController<any>
->
+export const controllerKey = '__vintl_controller'