We're preparing to move to main as default branch

Part of our prettier migration; changing the arrow-parens style.

We follow this imports order:
// 1. "external" modules
import _ from 'lodash';
import chalk from 'chalk';
// 2. "internal" and aliased modules
import foo from 'src/foo';
// 3. modules from a "parent" directory
import foo from '../foo';
import qux from '../../foo/qux';
// 4. "sibling" modules from the same or a sibling's directory
import bar from './bar';
import baz from './bar/baz';
// 5. "index" of the current directory
import main from './';

- Creates factory function for router that takes
  in a store reference.
- Updates store to use router module instead of
  reference to router singleton
- Use sync_router_and_store utility

This allows ide_router not to be coupled to a
singleton store instance, but accept this as
a parameter. This helps greatly with some test
set up and breaking the cyclical dependency.

Includes related import reordering for IDE-related
files to fix eslint warnings.

See issue https://gitlab.com/gitlab-org/gitlab/issues/29243
which tracks the overall effort for migration to Jest.