Part of apple/swift-openapi-generator#868

Remove usages of `NSLock` and vendor the lock from swift-nio instead.

Part of apple/swift-openapi-generator#868

Refactors `error.localizedDescription` to `"\(error)"` to prevent
linking Foundation. This will change the error strings as can be seen in
the tests. Alternatively, we would split the implementation by a trait
`FullFoundationSupport`. Where that would use `localizedDescription`

Part of apple/swift-openapi-generator#868

Removes usages of localized compares from Foundation and just uses Swift
string comparisons.

The logic is covered by the following tests:
```
Test_URICodingRoundtrip.testRoundtrip
Test_URISerializer.testSerializing
Test_ClientConverterExtensions.test_setOptionalRequestBodyAsURLEncodedForm_codable
Test_ClientConverterExtensions.test_setRequiredRequestBodyAsURLEncodedForm_codable
```

Part of apple/swift-openapi-generator#868

Removes usages of `trimmingCharacters(in:)` and replaced by simple Swift
implementation. I added some tests that verify the behaviour against
Foundation.

---------

Co-authored-by: Honza Dvorsky <honza@apple.com>

…ing (#176)

Part of apple/swift-openapi-generator#868

Introduces a Swift impl of `replacingOccurrences(of:with:)`,
`addingPercentEncoding` and `removingPercentEncoding`.

The percent encoding were inspired by impl in `swift-foundation`:
https://github.com/swiftlang/swift-foundation/blob/aee1d337039b5b2a1f0c3b7f83baa950dac3a84e/Sources/FoundationEssentials/URL/URLParser.swift

I also added tests to verify behaviour with Foundation.

Part of apple/swift-openapi-generator#868

Introduces a Swift-only impl of `String(format:)` that is only used in
`QualityValue.rawValue`.

---------

Co-authored-by: Honza Dvorsky <honza@apple.com>

Part of apple/swift-openapi-generator#868

This PR introduces a new default trait `FullFoundationSupport`. If users
remove this trait it does two things:
1. On non-darwin platforms it replaces the use of `ISO8601DateFormatter`
with the new Foundation APIs.
2. Disables support for `NSNull` and `NSNumber` in `OpenAPIValue`.

If non-darwin platforms disable this trait, its technically source
breaking if they rely on the initializer of `ISO8601DateTranscoder`,
because it relies on the `ISO8601DateFormatter.Options` object. I am not
sure how we would get around that. But again, it requires users to
explicitly remove the trait, and thereby want to opt in to only relying
on FoundationEssentials. So imo its acceptable.

I am not sure about CI. We really should be testing with and without the
trait, but I could not find other examples that use the swift-nio jobs
to do this. But if you could point me in the right direction, I can add
that as well.

From what I understand from @FranzBusch, we also only have 1 chance of
adding default traits. Are there any other traits we should think about
introducing?

---------

Co-authored-by: Honza Dvorsky <honza@apple.com>

…s imports (#180)

Fixes Windows build by making sure we can import CoreFoundation