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_mainloop/gui-gtk.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+"""Simple GTK example to manually test event loop integration.
+
+To run this:
+1) Enable the PyDev GUI event loop integration for gtk
+2) do an execfile on this script
+3) ensure you have a working GUI simultaneously with an
+   interactive console
+"""
+
+if __name__ == '__main__':
+    import pygtk
+    pygtk.require('2.0')
+    import gtk
+    
+    
+    def hello_world(wigdet, data=None):
+        print("Hello World")
+    
+    def delete_event(widget, event, data=None):
+        return False
+    
+    def destroy(widget, data=None):
+        gtk.main_quit()
+    
+    window = gtk.Window(gtk.WINDOW_TOPLEVEL)
+    window.connect("delete_event", delete_event)
+    window.connect("destroy", destroy)
+    button = gtk.Button("Hello World")
+    button.connect("clicked", hello_world, None)
+    
+    window.add(button)
+    button.show()
+    window.show()
+