This adds a swift Decoder that decodes from a swift-configuration
ConfigSnapshot, and adds the ability to modify how select types are
decoded within the
ConfigSnapshotDecoder. This is something that JSONEncoder already does
with URLs specifically, however this enables users to configure this
behavior for any arbitrary type regardless of existing Codable
conformance.
The decoder will help us expand on top of (pr:
https://github.com/apple/container/pull/1425), which switches user
configuration to TOML. With this PR we will be able to provide a multi
layered TOML if desired, allowing container to ship a default TOML
instead of encoding them in code constants.
Noah Thornton