Python: Add example of top-level module shadowing stdlib

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/README.md

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+This test shows how we handle modules the shadow a module in the standard library.
+
+We manually replicate the behavior of `codeql database create --source-root <src-dir>`, which will use `-R <src-dir>`. By default, the way qltest invokes the extractor will cause different behavior. Therefore, we also need to move our code outside of the top-level folder, and it lives in `code/`.
+
+Because we have a `cmd.py` file, whenever the python interpreter sees `import cmd`, that is the file that will be used! --
+
+* `python test_ok.py` works as intended, and prints `Foo`
+* `python test_fail.py` raises an exception, since it imports `pdb.py` from the standard library, which (at least in Python 3.8) tries to import `cmd.py` from the standard library, but instead is served our `cmd.py` module. Therefore it fails with `AttributeError: module 'cmd' has no attribute 'Cmd'`

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/ReferenceToLocalModule.ql

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+import python
+
+from ModuleValue project_module, ControlFlowNode ref, string part_of_project
+where
+  exists(project_module.getScope().getFile().getRelativePath()) and
+  ref = project_module.getAReference() and
+  (
+    exists(ref.getLocation().getFile().getRelativePath()) and
+    part_of_project = "is part of this projects code"
+    or
+    not exists(ref.getLocation().getFile().getRelativePath()) and
+    part_of_project = "is NOT part of this projects code"
+  )
+select "Local module '" + project_module.getName() + "' referenced in module '" +
+    ref.getEnclosingModule().getName() + "' which " + part_of_project

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code/cmd.py

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+foo = "Foo"
+print("my own cmd imported")

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code/test_fail.py

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+# we import `pdb` which import the `cmd` module from the standard library
+# and allows us to set --max-import-depth=2, to make the test run fast
+import pdb

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code/test_ok.py

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+from cmd import foo
+print(foo)

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/options

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+semmle-extractor-options: --max-import-depth=2 -R code/