feat: show new stop page layout & features

[thecristen]

Scope

Asana Ticket: TBA

Implementation

Using live_render/3 to embed LiveViews into a regular page

Note

This PR first fixes an issue where we couldn't use live_render/3. It turned out using different plugs for regular pages vs live view pages was making the root layout kind of confused and the security signature not matching, or something.
It's fixed by the first commit, which made the search bar break with a 403 error and necessitated the second commit:

• fix(DotcomWeb.Router): consolidate pipelines
• fix(autocomplete): send CSRF token in POST

All other POST requests seem to remain working as expected.

Kicking off the reworked Stop Page

• Created a feature flag
• Use the feature flag to toggle between old and new layouts

Changed in both versions: Some styling tweaks shared between both, mostly the heading sizes

Added in new layout

• The basic side-by-side structure, with Upcoming Departures at top in the mobile breakpoint
• Refactored the existing StopMapLive LiveView and added it to the new page where the map goes (thanks @joshlarson for the prior art in feat: Add a preview page with a stop map #2806 !)
• Stubbed out another LiveView for the Upcoming Departures piece

Screenshots

Normal	With Feature Flag

How to test

Try with and without the feature flag

---

• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1218398178190666