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_coverage.py

@@ -0,0 +1,94 @@
+'''
+Entry point module to run code-coverage.
+'''
+
+
+def is_valid_py_file(path):
+    '''
+    Checks whether the file can be read by the coverage module. This is especially
+    needed for .pyx files and .py files with syntax errors.
+    '''
+    import os
+
+    is_valid = False
+    if os.path.isfile(path) and not os.path.splitext(path)[1] == '.pyx':
+        try:
+            with open(path, 'rb') as f:
+                compile(f.read(), path, 'exec')
+                is_valid = True
+        except:
+            pass
+    return is_valid
+
+
+def execute():
+    import os
+    import sys
+
+    files = None
+    if 'combine' not in sys.argv:
+
+        if '--pydev-analyze' in sys.argv:
+
+            # Ok, what we want here is having the files passed through stdin (because
+            # there may be too many files for passing in the command line -- we could
+            # just pass a dir and make the find files here, but as that's already
+            # given in the java side, let's just gather that info here).
+            sys.argv.remove('--pydev-analyze')
+            s = input()
+            s = s.replace('\r', '')
+            s = s.replace('\n', '')
+
+            files = []
+            invalid_files = []
+            for v in s.split('|'):
+                if is_valid_py_file(v):
+                    files.append(v)
+                else:
+                    invalid_files.append(v)
+            if invalid_files:
+                sys.stderr.write('Invalid files not passed to coverage: %s\n'
+                                 % ', '.join(invalid_files))
+
+            # Note that in this case we'll already be in the working dir with the coverage files,
+            # so, the coverage file location is not passed.
+
+        else:
+            # For all commands, the coverage file is configured in pydev, and passed as the first
+            # argument in the command line, so, let's make sure this gets to the coverage module.
+            os.environ['COVERAGE_FILE'] = sys.argv[1]
+            del sys.argv[1]
+
+    try:
+        import coverage  # @UnresolvedImport
+    except:
+        sys.stderr.write('Error: coverage module could not be imported\n')
+        sys.stderr.write('Please make sure that the coverage module '
+                         '(http://nedbatchelder.com/code/coverage/)\n')
+        sys.stderr.write('is properly installed in your interpreter: %s\n' % (sys.executable,))
+
+        import traceback;traceback.print_exc()
+        return
+
+    if hasattr(coverage, '__version__'):
+        version = tuple(map(int, coverage.__version__.split('.')[:2]))
+        if version < (4, 3):
+            sys.stderr.write('Error: minimum supported coverage version is 4.3.'
+                             '\nFound: %s\nLocation: %s\n'
+                             % ('.'.join(str(x) for x in version), coverage.__file__))
+            sys.exit(1)
+    else:
+        sys.stderr.write('Warning: Could not determine version of python module coverage.'
+                         '\nEnsure coverage version is >= 4.3\n')
+
+    from coverage.cmdline import main  # @UnresolvedImport
+
+    if files is not None:
+        sys.argv.append('xml')
+        sys.argv += files
+
+    main()
+
+
+if __name__ == '__main__':
+    execute()