Replaces all the foundation imports.
One issue is that `HTTPClient.init?(httpsURLWithSocketPath socketPath:
String, uri: String = "/")` uses `addingPercentEncoding()` from
Foundation. So instead, we use a pure Swift impl. that does the same.
We also need to disable default traits from `swift-configuration` to
prevent linking Foundation, because the `JSON` trait does that.
This also adds a linkage test to prevent regressions to CI.
* make `Scheme` a type
* introduce new Endpoint type
* use endpoint as storage in `HTTPClient.Request`
* fix merge conflicts
* rename Endpoint to DeconstructedURL
* swift-format
* make `DeconstructedURL` properties `var`'s
* move scheme into global namespace
- rename `useTLS` to `usesTLS` where posible without breaking public API
- only import Foundation.URL
* fix review comments