gh-127111: Emscripten Make web example work again (#127113)

Moves the Emscripten web example into a standalone folder, and updates 
Makefile targets to build the web example. Instructions for usage have
also been added.

Tools/wasm/emscripten/web_example/server.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+import argparse
+from http import server
+
+parser = argparse.ArgumentParser(
+    description="Start a local webserver with a Python terminal."
+)
+parser.add_argument(
+    "--port", type=int, default=8000, help="port for the http server to listen on"
+)
+parser.add_argument(
+    "--bind", type=str, default="127.0.0.1", help="Bind address (empty for all)"
+)
+
+
+class MyHTTPRequestHandler(server.SimpleHTTPRequestHandler):
+    def end_headers(self) -> None:
+        self.send_my_headers()
+        super().end_headers()
+
+    def send_my_headers(self) -> None:
+        self.send_header("Cross-Origin-Opener-Policy", "same-origin")
+        self.send_header("Cross-Origin-Embedder-Policy", "require-corp")
+
+
+def main() -> None:
+    args = parser.parse_args()
+    if not args.bind:
+        args.bind = None
+
+    server.test(  # type: ignore[attr-defined]
+        HandlerClass=MyHTTPRequestHandler,
+        protocol="HTTP/1.1",
+        port=args.port,
+        bind=args.bind,
+    )
+
+
+if __name__ == "__main__":
+    main()