Following feedback from @benrimmington in https://github.com/apple/swift-collections/pull/607, this changes the following: 1. Uses `objectFormat()` compiler conditional instead of `os()` (see "Cross-platform object file format support" in [SE-0492](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0492-section-control.md#cross-platform-object-file-format-support)) 2. Uses a raw identifier for the generated Swift symbol name, instead of an escaped name (see [SE-0451](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0451-escaped-identifiers.md))