refactor(TripPlannerForm): use LiveComponent

[thecristen]

Asana Ticket: LiveView-compatible trip planner form inputs

This is primarily a refactor of the trip planner form, from using a functional component to a Phoenix.LiveComponent.

Highlights:

• Improvements to validation: checks whether the field is touched before rendering any errors. Also should eagerly revalidate (e.g. as soon as you fill in the field the error will disappear, as opposed to leaving the error on screen until resubmitting the form)
• Datetime selection
  • The datepicker toggles visibility when choosing between now/arrive/depart
  • The form will always set the chosen datetime to the current date and time if "now" is selected, otherwise it'll validate whether the datetime is in the past
• Mode selection
  • Verifies whether at least one mode is present
  • Adjusts the accordion text based on selected modes

Other changes:

• Uses several components from MbtaMetro, so this PR installs and sets this up as well.
  • Adjusts our Tailwind configuration:
    • Follows the guidance from MbtaMetro
    • Adds two class names to the blocklist since they conflict with our existing Bootstrap styles in terrible ways
    • Adds important: true
  • Thanks to the prior two bulletpoints: our CSS now imports the base Tailwind CSS
  • Removes our CoreComponents
• Sets up Phoenix verified routes so I can use ~p in a test