Reintroduce re-exports in rhai::plugin

[Abendrill]

This PR re-introduce some re-exports that were removed from rhai::plugin in 1.25.0.

This removal was an unintended breaking change despite the items still being available, since dependent crates may have used this import path. In-fact, this did break apollo-router when used as a library.

Fixes #1098

[schungx]

The formatting CI is failing... Perhaps you need to do a cargo fmt.

[Abendrill]

My bad, I've applied formatting now.

❗ Also two ui_tests failed. rustc decided to use std::iter::Iterator instead of just Iterator. I'm not sure why. I just opted to update the expected output. Are you @schungx ok with this?

[schungx]

I think you should remove the fixes to the unrelated tests as it'd just clutter up the PR.

I'd put in another PR later on to fix the test outputs.

Don't worry if they fail at this point.

[Abendrill]

Alright, will do.

[schungx]

Yes because Rust 1.90 has just come out and there would be more test outputs that need to update anyway.

[Abendrill]

Removed the ui_test changes now!

[Abendrill]

Thanks for quick and responsive collab @schungx! 🚀