fix(TripPlan.InputForm): improve location validation + add visual error state

[thecristen]

Summary of changes

Asana Ticket: mostly TP | Add an error state when location isn't selected with some UI/UX | Trip Planner location input error state, should fix TP Bugs | Trip planner input location bug

Will be even better with #2364 and #2361 in the mix.

Key changes

• Validation of the :to and :from fields has been overhauled, and adds the error where needed
• The location inputs are technically themable now, and we use that to change to the error styling when that form field has errors
• Text that's pasted into the location inputs now gets sent to LiveView (as a pseudo-"selection" that's a name with no lat/lon) and proceeds through our usual pipelines

More changes

• Fixes the default params in Dotcom.TripPlan.AntiCorruptionLayer to not encode missing params as "nil"
• Only validates whether locations A != B if each location is itself valid

[joshlarson]

The UX for this looks great!

I think it'd be worth having a test ensuring that there's an error when a location is invalid, and that there is no error when the location is just fully absent (I think that test would be at the Dotcom.TripPlan.InputForm level?)

[thecristen]

@joshlarson Great! I've added a test for the first thing; the second thing already has a test for no error when the location is fully absent!

[joshlarson]

🐈

[joshlarson]

🐈‍⬛