JSPI and dynamic linking messed up by stub trampoline

[hoodmane]

The dynamic linking code will generate a stub if it's not resolved when first imported:

          // Return a stub function that will resolve the symbol
          // when first called.
          if (!(prop in stubs)) {
            var resolved;
            stubs[prop] = (...args) => {
              resolved ||= resolveSymbol(prop);
              return resolved(...args);
            };
          }

https://github.com/emscripten-core/emscripten/blob/main/src/library_dylink.js?plain=1#L724-L727
This causes trouble when mixed with stack switching. Working around it will be a bit convoluted, but it should be possible with a little helper wasm module.