starship: add presets option

[bandithedoge]

Description

Fixes #7297. Mirrors NixOS/nixpkgs@68543ba.

I'm not sure how to do test cases that don't have to be manually updated along with Starship. Is it alright to use IFD in the test and compare attrsets parsed from TOML?

Checklist

• Change is backwards compatible.

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• Test cases updated/added. See example.

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[teto]

it's not a crucial setting so it's fine if not tested. IFD in tests would be fine I beleive. If someone can confirm it works, we can merge as is

[Invizory]

If someone can confirm it works, we can merge as is

Works for me :)

[khaneliman]

IFD in tests would be fine I beleive.

Ideally, used nowhere..realistically, it's probably fine in tests since it won't leak IFD into a user eval and just be a contributor limitation. But, we have them guarded atm behind a flag to prevent people from being blocked on contributing due to IFD. #6905 introduced the argument to guard IFD as opt-in

[Invizory]

Is something still blocking this PR from merging?

[bandithedoge]

Not that I'm aware of.