Mangling doesn't handle local archetypes

[hamishknight]

The following test case crashes SourceKit:

func foo<each T>(_ xs: repeat each T) {
  for x in repeat each xs {
    // RUN: %sourcekitd-test -req=cursor -pos=%(line-1):7 %s -- %s
  }
}

{
  key.request: source.request.cursorinfo,
  key.offset: 2767,
  key.sourcefile: "/Users/hamish/src/swift-test-arena/swift-test-arena/main.swift",
  key.primary_file: "/Users/hamish/src/swift-test-arena/swift-test-arena/main.swift",
  key.compilerargs: [
    "/Users/hamish/src/swift-test-arena/swift-test-arena/main.swift"
  ]
}
Cannot mangle free-standing archetype: (element_archetype_type address=0x11ea0baa0 conforms_to="Swift.(file).Copyable" conforms_to="Swift.(file).Escapable" opened_element_id="7F7D30B0-D452-11EF-BBBD-4A10B34A40AC")
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      While evaluating request USRGenerationRequest(main.(file).foo(_:).x@/Users/hamish/src/swift-test-arena/swift-test-arena/main.swift:168:7)
fish: Job 1, './sourcekitd-test -req=cursor -…' terminated by signal SIGABRT (Abort)

Swift version 6.2-dev (LLVM bb5a46203470a96, Swift 192bb334093ddfa)
Target: arm64-apple-darwin24.2.0

[hamishknight]

This also affects regular compilation for cases like:

func foo<each T>(_ xs: repeat each T) {
  for x in repeat each xs {
    lazy var y = x
  }
}