ui(TripPlanner): Make <.itinerary_detail /> more closely match final designs

[joshlarson]

Before

After

Summary of changes

Asana Tickets:

• Improve route line connection to icons
• Flip the expand walking/transit directions caret

Visual Changes

• Route-color line on transit legs goes fully connects the bus or T stop icons
• Transit legs now have rounded corners
• Slight changes in icon sizing (walk icon is bigger - stop icons are smaller)
• Stop/Station icons stick to the tops of their containers, rather than getting centered.

Under-the-hood Changes

• All of the layout is flex now instead of grid.
• Refactored to tease apart <.place /> and <.start_or_end_place /> - <.place /> no longer has the background logic anymore (that's handled by <.transit_leg /> and <.start_or_end_place />, and the icons are passed into it via a slot.

TODO

• Restore the wheelchair icon for station places
• Restore link functionality (ideally having it open in a new tab)
• Don't show the chevron on transit leg details when there's nothing to expand/collapse
• Fix padding and spacing around alerts
• Double-check font sizes
• Make icons shrink-0 instead of wrapping them in <div />'s
• Fix "Ride the Orange Line train 3 stops" Follow up
• Fix spacing for transit leg icons Follow up

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General checks

• Are the changes organized into self-contained commits with descriptive and well-formatted commit messages? This is a good practice that can facilitate easier reviews.
• Testing. Do the changes include relevant passing updates to tests? This includes updating screenshots. Preferably tests are run locally to verify that there are no test failures created by these changes, before opening a PR.
• Tech debt. Have you checked for tech debt you can address in the area you're working in? This can be a good time to address small issues, or create Asana tickets for larger issues.

[thecristen]

the tiniest change!!