chore: improve expression types

[GerkinDev]

Joi.expression did not accept functions record, and returned any.

[Marsup]

Thanks for the PR. I'm not exactly sure what it's fixing, maybe it would be worth adding a quick test (in test/index.ts) to ensure there's no regression in the future?

[davidjamesstone]

@Marsup this PR fixes this issue with the types around LanguageMessages and Expressions.

The 2nd arg of Joi.expression should allow for a functions map to be passed.

Also, LanguageMessages should allow Joi.expressions as the Record value.

[GerkinDev]

I added the test. It fixes what @davidjamesstone mentioned, so it closes #3064

[Marsup]

I'm not yet sure what's the problem with the tests, the error line doesn't match, I'm investigating.

[Marsup]

OK, it's because of your render function calls, I'm honestly not sure it should be exposed, as the state is kind of hard to recreate from outside of joi.

[GerkinDev]

What shouldn't be exposed ?