Sighting GPS location widget

[achou11]

Closes #33

Notes:

• Introduces a new dependency: Flutter MapLibre GL

• we're currently using the default map style that comes from the MapLibreGL project. It's very barebones and we probably should not stick with it in the long term due to (presumable) maintenance burden for them and also lack of detail in general. we should decide on a map provider or look into implementing offline maps (which is more work)

• as a follow-up, in the case that we're using online map styles+tiles, it would make sense to create a setting that defines the style URL for the maps to use. the reason for doing this instead of hardcoding the url somewhere in the app code is to mitigate usability issues in the case of a service outage or a mishap with the access token. We made this mistake at my work recently (we rotated an API key by accident) and the only way to unbreak maps on peoples' devices was to do another release of the app. with the settings-based approach, users can at least insert another URL (whether it be for another map provider or the same one but with a working API key) and not have to wait on the devs to fix the app code and make an app release.

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Preview

End-to-end flow:

had to split it up due to video size limits

Part 1:

location_field_1.mp4

Part 2:

location_field_2.mp4

Screenshots:

• Read mode when:

  • location is set:

    

  • location is not set:

    

• Edit mode when:

  • location is set:

    (before pressing map)

    

    (after pressing map)

    

  • location is not set: