gh-124621: Emscripten: Add support for async input devices (GH-136822)

This is useful for implementing proper `input()`. It requires the
JavaScript engine to support the wasm JSPI spec which is now stage 4.
It is supported on Chrome since version 137 and on Firefox and node
behind a flag.

We override the `__wasi_fd_read()` syscall with our own variant that
checks for a readAsync operation. If it has it, we use our own async
variant of `fd_read()`, otherwise we use the original `fd_read()`.
We also add a variant of `FS.createDevice()` called
`FS.createAsyncInputDevice()`.

Finally, if JSPI is available, we wrap the `main()` symbol with
`WebAssembly.promising()` so that we can stack switch from `fd_read()`.
If JSPI is not available, attempting to read from an AsyncInputDevice
will raise an `OSError`.

Tools/wasm/emscripten/__main__.py

@@ -263,10 +263,20 @@ def configure_emscripten_python(context, working_dir):
                 REALPATH=abs_path
             fi
 
+            # Before node 24, --experimental-wasm-jspi uses different API,
+            # After node 24 JSPI is on by default.
+            ARGS=$({host_runner} -e "$(cat <<"EOF"
+            const major_version = Number(process.version.split(".")[0].slice(1));
+            if (major_version === 24) {{
+                process.stdout.write("--experimental-wasm-jspi");
+            }}
+            EOF
+            )")
+
             # We compute our own path, not following symlinks and pass it in so that
             # node_entry.mjs can set sys.executable correctly.
             # Intentionally allow word splitting on NODEFLAGS.
-            exec {host_runner} $NODEFLAGS {node_entry} --this-program="$($REALPATH "$0")" "$@"
+            exec {host_runner} $NODEFLAGS $ARGS {node_entry} --this-program="$($REALPATH "$0")" "$@"
             """
         )
     )