Extract mangled names from .swiftinterface rather than using nm

[DougGregor]

The Swift compiler recently added a frontend option (in swiftlang/swift#76600) -abi-comments-in-module-interface that emits ABI-related comments into the generated Swift interface file. Parse the resulting // MANGLED NAME: comments to extract mangled name information for public symbols instead of relying on hardcoded nm invocations on the shared library.

Note that this pull request means that jextract-swift will require an as-yet-unreleased Swift compiler that comes from the main branch. At present, there is no downloadable toolchain containing the compiler fix, so I'm starting by opening this as a draft. Once downloadable toolchains are available for all platforms, we can update the documentation to point jextract-swift users there and merge this pull request.

Remove all of the supporting code for querying nm, which turns out to be a lot :).

[ktoso]

LGTM thanks! Great to get rid of the vendored-in subprocess (and nm hack 😉)

Waiting for a toolchain then... 🕐

[ktoso]

Sorry for the conflicts, but should be easy to resolve -- it's the to-be-removed subprocess mostly 🙇

[DougGregor]

Sorry for the conflicts, but should be easy to resolve -- it's the to-be-removed subprocess mostly 🙇

No worries! The conflicts are all easy to resolve when it's time.

[ktoso]

Look at who's passing on Linux:

MySwiftClassTest > test_MySwiftClass_voidMethod() STANDARD_OUT
    [java][MySwiftClass.java:131] Downcall: <init>(12, 42)
    [java][MySwiftClass.java:528] Downcall: voidMethod(MemorySegment{ address: 0x7f337c92b620, byteSize: 0 })

MySwiftClassTest > test_MySwiftClass_makeIntMethod() STANDARD_OUT
    [java][MySwiftClass.java:131] Downcall: <init>(12, 42)
    [java][MySwiftClass.java:736] Downcall: makeIntMethod(MemorySegment{ address: 0x7f337c92c030, byteSize: 0 })

and all of its friends 😄