[Web] Add the "serve" and "run" scons targets.

You can now run the test HTTP server by calling:

scons p=javascript serve

If you also wish to run the browser, call instead:

scons p=javascript run

The default listen port is 8060, but can be overriden via the env
variable GODOT_WEB_TEST_PORT which must be a valid integer.

(cherry picked from commit a06602363c9b001a1877afa771b3282f2230595c)

platform/javascript/SCsub

@@ -2,6 +2,20 @@
 
 Import("env")
 
+# The HTTP server "targets". Run with "scons p=javascript serve", or "scons p=javascript run"
+if "serve" in COMMAND_LINE_TARGETS or "run" in COMMAND_LINE_TARGETS:
+    from serve import serve
+    import os
+
+    port = os.environ.get("GODOT_WEB_TEST_PORT", 8060)
+    try:
+        port = int(port)
+    except Exception:
+        print("GODOT_WEB_TEST_PORT must be a valid integer")
+        sys.exit(255)
+    serve(env.Dir("#bin/.javascript_zip").abspath, port, "run" in COMMAND_LINE_TARGETS)
+    sys.exit(0)
+
 javascript_files = [
     "audio_driver_javascript.cpp",
     "godot_webgl2.cpp",

platform/javascript/serve.py

@@ -24,6 +24,17 @@ def shell_open(url):
         subprocess.call([opener, url])
 
 
+def serve(root, port, run_browser):
+    os.chdir(root)
+
+    if run_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:{port}")
+
+    test(CORSRequestHandler, HTTPServer, port=port)
+
+
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
     parser.add_argument("-p", "--port", help="port to listen on", default=8060, type=int)
@@ -41,12 +52,4 @@ if __name__ == "__main__":
     # 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)
+    serve(args.root, args.port, args.browser)