Create IDE router module

- This is to help decouple the store from the router instance
- Instead of making direct calls, we'll update state and the
  router will react to the state change

app/assets/javascripts/ide/stores/modules/router/actions.js

+import * as types from './mutation_types';
+
+// eslint-disable-next-line import/prefer-default-export
+export const push = ({ commit }, fullPath) => {
+  commit(types.PUSH, fullPath);
+};

app/assets/javascripts/ide/stores/modules/router/index.js

+import state from './state';
+import mutations from './mutations';
+import * as actions from './actions';
+
+export default {
+  namespaced: true,
+  state,
+  mutations,
+  actions,
+};

app/assets/javascripts/ide/stores/modules/router/mutation_types.js

+// eslint-disable-next-line import/prefer-default-export
+export const PUSH = 'PUSH';

app/assets/javascripts/ide/stores/modules/router/mutations.js

+import * as types from './mutation_types';
+
+export default {
+  [types.PUSH](state, fullPath) {
+    state.fullPath = fullPath;
+  },
+};

app/assets/javascripts/ide/stores/modules/router/state.js

+export default () => ({
+  fullPath: '',
+});

spec/frontend/ide/stores/modules/router/actions_spec.js

+import * as actions from '~/ide/stores/modules/router/actions';
+import * as types from '~/ide/stores/modules/router/mutation_types';
+import testAction from 'helpers/vuex_action_helper';
+
+const TEST_PATH = 'test/path/abc';
+
+describe('ide/stores/modules/router/actions', () => {
+  describe('push', () => {
+    it('commits mutation', () => {
+      return testAction(
+        actions.push,
+        TEST_PATH,
+        {},
+        [{ type: types.PUSH, payload: TEST_PATH }],
+        [],
+      );
+    });
+  });
+});

spec/frontend/ide/stores/modules/router/mutations_spec.js

+import mutations from '~/ide/stores/modules/router/mutations';
+import * as types from '~/ide/stores/modules/router/mutation_types';
+import createState from '~/ide/stores/modules/router/state';
+
+const TEST_PATH = 'test/path/abc';
+
+describe('ide/stores/modules/router/mutations', () => {
+  let state;
+
+  beforeEach(() => {
+    state = createState();
+  });
+
+  describe(types.PUSH, () => {
+    it('updates state', () => {
+      expect(state.fullPath).toBe('');
+
+      mutations[types.PUSH](state, TEST_PATH);
+
+      expect(state.fullPath).toBe(TEST_PATH);
+    });
+  });
+});