Vendor debugpy for VS Code attach debugging

Bundles debugpy 1.7.0 directly in python/ so "Maya: Attach (debugpy)"
works with no per-machine pip install step. Installed via Maya 2022's
own pip so it resolved a version actually compatible with Python 3.7
(Maya 2022's interpreter), then verified import + listen() succeeds
under all three target Maya Python versions (3.7/3.9/3.10).

Also fixes a latent __file__-under-exec() bug in
start_debug_server.py (same pitfall as Maya's own plugin loader,
never hit until this exercised it) and corrects the README's Maya
Python version claim -- 2022 ships Python 3.7, not 3.9 as previously
stated, which was never independently verified until now.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

python/debugpy/_vendored/pydevd/tests_python/flask1/app.py

@@ -0,0 +1,60 @@
+from flask import Flask
+from flask import render_template
+
+app = Flask(__name__)
+
+
+@app.route("/")
+def home():
+    content = 'Flask-Jinja-Test'
+    return render_template(
+        "hello.html",
+        title='Hello',
+        content=content
+    )
+
+
+@app.route("/handled")
+def bad_route_handled():
+    try:
+        raise ArithmeticError('Hello')
+    except Exception:
+        pass
+    return render_template(
+        "hello.html",
+        title='Hello',
+        content='Flask-Jinja-Test'
+    )
+
+
+@app.route("/unhandled")
+def bad_route_unhandled():
+    raise ArithmeticError('Hello')
+    return render_template(
+        "hello.html",
+        title='Hello',
+        content='Flask-Jinja-Test'
+    )
+
+
+@app.route("/bad_template")
+def bad_template():
+    return render_template(
+        "bad.html",
+        title='Bad',
+        content='Flask-Jinja-Test'
+    )
+
+
+@app.route("/exit")
+def exit_app():
+    from flask import request
+    func = request.environ.get('werkzeug.server.shutdown')
+    if func is None:
+        raise RuntimeError('No shutdown')
+    func()
+    return 'Done'
+
+
+if __name__ == '__main__':
+    app.run()