feat!: make router a separate plugin (#4196)

* refactor: move router to its own plugin

* refactor: rename routerHistoryMode option to historyMode

* test: add @vue/cli-plugin-router tests

* feat: change src/router.js for most common use cases

* fix: fix cli-ui tests

* docs: Remove router root option from docs

* fix: add support for legacy router option

docs/dev-guide/ui-api.md

@@ -1274,7 +1274,7 @@ const ROUTER = 'vue-router-add'
 
 api.onViewOpen(({ view }) => {
   if (view.id === 'vue-project-plugins') {
-    if (!api.hasPlugin('vue-router')) {
+    if (!api.hasPlugin('router')) {
       api.addSuggestion({
         id: ROUTER,
         type: 'action',
@@ -1282,7 +1282,7 @@ api.onViewOpen(({ view }) => {
         message: 'org.vue.cli-service.suggestions.vue-router-add.message',
         link: 'https://router.vuejs.org/',
         async handler () {
-          await install(api, 'vue-router')
+          await install(api, 'router')
         }
       })
     }