Revert "Revert "refactor: move common/lib/capa/capa to xmodule/capa" (#30762)"

This reverts commit 4463ee751d.

docs/guides/testing/testing.rst

@@ -71,7 +71,7 @@ Test Locations
 
 -  Python unit and integration tests: Located in subpackages called
    ``tests``. For example, the tests for the ``capa`` package are
-   located in ``common/lib/capa/capa/tests``.
+   located in ``xmodule/capa/tests``.
 
 -  Javascript unit tests: Located in ``spec`` folders. For example,
    ``xmodule/js/spec`` and
@@ -432,7 +432,7 @@ Factories are often implemented using `FactoryBoy`_.
 
 In general, factories should be located close to the code they use. For
 example, the factory for creating problem XML definitions is located in
-``common/lib/capa/capa/tests/response_xml_factory.py`` because the
+``xmodule/capa/tests/response_xml_factory.py`` because the
 ``capa`` package handles problem XML.
 
 .. _FactoryBoy: https://readthedocs.org/projects/factoryboy/