New KeyValuePairs view

[karwa]

TODO:

• [x] Format tests.
• [ ] Make sure there are tests for semicolons in content being automatically encoded when using ExtendedForm schema.
• [ ] Allow the schema to decide whether non-URL-code-points are escaped. On the one hand, it's not really the schema's business, but on the other hand, it kinda is, because it means those code-points can't be used as an escapable subcomponent delimiter.
• [ ] Pin the Apple build-only CI to a specific Xcode version

[karwa]

Ugh the reason for the failing "build-only macos" build (error: cannot specialize protocol type 'Collection') is that it uses the default Xcode version, which on GHA runners is 14.0.1 for the next few days at least.

Xcode 14.0.1 includes the swift 5.7 compiler, so the #if swift(>=5.7) check passes, but it only includes the macOS 12.5 SDK, so it comes with an old copy of the standard library without primary associated type definitions.

This doesn't affect any other platform, and it's not really important to support Xcode 14.0.1 specifically, so I think we'll just wait it out. Eventually GHA runners will be updated and we can just not support the weird configuration on this particular version of Xcode.