PackageToJS: Derive WASI and shared memory support from wasm imports - #807

The SwiftBuild backend's build directory doesn't encode the target triple, so
detect the traits derived from it by parsing the imports of the product binary
instead. The imports are now parsed as a part of the packaging build graph.

```
$ echo "@preconcurrency import var Foundation.stderr" | swiftly run +main-snapshot-2026-08-11 swiftc  - -o /dev/null
<stdin>:1:28: error: ambiguous name 'stderr' in module 'Foundation'
1 | @preconcurrency import var Foundation.stderr
  |                            `- error: ambiguous name 'stderr' in module 'Foundation'
2 |

Glibc.stderr:1:32: note: found this candidate
1 | nonisolated(unsafe) public var stderr: UnsafeMutablePointer<FILE>! { get }
  |                                `- note: found this candidate

/usr/include/stdio.h:151:14: note: found this candidate
149 | extern FILE *stdin;               /* Standard input stream.  */
150 | extern FILE *stdout;              /* Standard output stream.  */
151 | extern FILE *stderr;              /* Standard error output stream.  */
    |              `- note: found this candidate
152 | /* C89/C99 say they're macros.  Make them happy.  */
153 | #define stdin stdin
```

swiftlang/swift#89891