[WebAssembly] Add symbol information for shared libraries (#75238)

The current (experimental) spec for WebAssembly shared libraries does
not include a full symbol table like the object format. This change
extracts symbol information from the normal wasm exports.

This is the first step in having the linker report undefined symbols
when linking with shared libraries. The current behaviour is to ignore
all undefined symbols when linking with `-pie` or `-shared`.

See https://github.com/emscripten-core/emscripten/issues/18198