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/pydev_ipython/README

@@ -0,0 +1,8 @@
+# Parts of IPython, files from: https://github.com/ipython/ipython/tree/rel-1.0.0/IPython
+# The files in this package are extracted from IPython to aid the main loop integration
+# See tests_mainloop for some manually runable tests
+
+# What we are doing is reusing the "inputhook" functionality (i.e. what in IPython
+# ends up on PyOS_InputHook) and using it in the pydevconsole context.
+# Rather that having the callbacks called in PyOS_InputHook, we use a custom XML-RPC
+# Server (HookableXMLRPCServer) that calls the inputhook when idle