Replace local web server setup for web editor with a Python-based solution

This makes it easier to set up, as you always have Python installed
when building Godot. On the other hand, you don't always have Node.js
+ npm installed (and you may not want to spend time running `npm install`).

Co-authored-by: Fabio Alessandrelli <fabio.alessandrelli@gmail.com>
(cherry picked from commit 1be1b15a57)

platform/javascript/serve.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python3
+
+from http.server import HTTPServer, SimpleHTTPRequestHandler, test  # type: ignore
+from pathlib import Path
+import os
+import sys
+import argparse
+import subprocess
+
+
+class CORSRequestHandler(SimpleHTTPRequestHandler):
+    def end_headers(self):
+        self.send_header("Cross-Origin-Opener-Policy", "same-origin")
+        self.send_header("Cross-Origin-Embedder-Policy", "require-corp")
+        self.send_header("Access-Control-Allow-Origin", "*")
+        super().end_headers()
+
+
+def shell_open(url):
+    if sys.platform == "win32":
+        os.startfile(url)
+    else:
+        opener = "open" if sys.platform == "darwin" else "xdg-open"
+        subprocess.call([opener, url])
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-p", "--port", help="port to listen on", default=8060, type=int)
+    parser.add_argument(
+        "-r", "--root", help="path to serve as root (relative to `platform/web/`)", default="../../bin", type=Path
+    )
+    browser_parser = parser.add_mutually_exclusive_group(required=False)
+    browser_parser.add_argument(
+        "-n", "--no-browser", help="don't open default web browser automatically", dest="browser", action="store_false"
+    )
+    parser.set_defaults(browser=True)
+    args = parser.parse_args()
+
+    # Change to the directory where the script is located,
+    # so that the script can be run from any location.
+    os.chdir(Path(__file__).resolve().parent)
+
+    if args.root:
+        os.chdir(args.root)
+
+    if args.browser:
+        # Open the served page in the user's default browser.
+        print("Opening the served URL in the default browser (use `--no-browser` or `-n` to disable this).")
+        shell_open(f"http://127.0.0.1:{args.port}")
+
+    test(CORSRequestHandler, HTTPServer, port=args.port)