Add type tests for Primer colors for `border*Color` properties

[gr2m]

follow up to #3619

@mattcosta7 shared some details

there are some other type-tests in the repo. I think since we're exposing a type that used in many places, it would be good to have some way to validate it, and ensure it's inclusive of all possible options.

I don't think tsd is used in the repo, but might be valuable to add something like it for type only assertions?

right now I think most type tests just ensure functions compile correctly - there's a bunch of files with .types.test suffixes where we do type only tests

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