[Runtime] Async bodies + swift-http-types adoption

[czechboy0]

Motivation

Runtime changes of the approved proposals apple/swift-openapi-generator#255 and apple/swift-openapi-generator#254.

Blockers of merging this

• 1.0 of swift-http-types

Modifications

⚠️ Contains breaking changes, this will land to main and then 0.3.0 will be tagged, so not backwards compatible with 0.2.0.

• add a dependency on https://github.com/apple/swift-http-types
• remove our currency types Request, Response, HeaderField
• replace them with the types provided by HTTPTypes
• remove ...AsString and the whole string-based serialization strategy, which was only ever used by bodies, but with streaming, we can't safely stream string chunks, only byte chunks, so we instead provide utils on HTTPBody to create it from string, and to collect it into a string. This means that the underlying type for the text/plain content type is now HTTPBody (a sequence of byte chunks) as opposed to String
• adapted Converter extensions to work with the new types
• added some internal utils for working with the query section of a path, as HTTPTypes doesn't provide that, the path property contains both the path and the query components (in setEscapedQueryItem)
• adapted error types
• adapted printing of request/response types, now no bytes of the body are printed, as they cannot be assumed to be consumable more than once
• adjusted the transport and middleware protocols, as described in the proposal
• removed the queryParameters property from ServerRequestMetadata, as now we parse the full query ourselves, instead of relying on the server transport to do it for us
• removed RouterPathComponent as now we pass the full path string to the server transport in the register function, allowing transport with more flexible routers to handle mixed path components, e.g. /foo/{bar}.zip.
• introduced HTTPBody, as described by the proposal
• adjusted UniversalClient and UniversalServer
• moved from String to Substring in a few types, to allow more passthrough of parsed string data without copying

Result

SOAR-0004 and SOAR-0005 implemented.

Test Plan

Introduced and adjusted tests for all of the above.

[czechboy0]

Ok, applied most of your feedback, @simonjbeaumont, and left some questions asking for clarification.

[simonjbeaumont]

Looks great, @czechboy0! Really nice work. Great attention to detail with docs and tests.