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-qt.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python
+"""Simple Qt4 example to manually test event loop integration.
+
+To run this:
+1) Enable the PyDev GUI event loop integration for qt
+2) do an execfile on this script
+3) ensure you have a working GUI simultaneously with an
+   interactive console
+
+Ref: Modified from http://zetcode.com/tutorials/pyqt4/firstprograms/
+"""
+
+if __name__ == '__main__':
+    import sys
+    from PyQt4 import QtGui, QtCore
+    
+    class SimpleWindow(QtGui.QWidget):
+        def __init__(self, parent=None):
+            QtGui.QWidget.__init__(self, parent)
+    
+            self.setGeometry(300, 300, 200, 80)
+            self.setWindowTitle('Hello World')
+    
+            quit = QtGui.QPushButton('Close', self)
+            quit.setGeometry(10, 10, 60, 35)
+    
+            self.connect(quit, QtCore.SIGNAL('clicked()'),
+                         self, QtCore.SLOT('close()'))
+    
+    if __name__ == '__main__':
+        app = QtCore.QCoreApplication.instance()
+        if app is None:
+            app = QtGui.QApplication([])
+    
+        sw = SimpleWindow()
+        sw.show()