Directive `.. autoapiclass` does not respect `autoapi_member_order = "bysource"`

[astrojuanlu]

As per title: directive .. autoapiclass does not respect autoapi_member_order = "bysource", and I'm not sure if there are others.

Here is a minimal working example: https://github.com/astrojuanlu/sphinx-autoapi-debug/tree/033f68fd

Even though testpkg.A has members c, a and b defined in this order, the rendered documentation gives a, b, and c:

Other things I found along the way:

• Initially I wrote autoapi_dirs = [""] by mistake, and .. autoapiclass:: testpkg.A didn't even give a warning. That made debugging more difficult.
• I get several warnings saying duplicate object description, probably because of the generated autoapi/testpkg/index.rst (don't think this is unheard of, but at the moment I can't locate what would be the best way to avoid them):

$ make html
Running Sphinx v4.4.0
loading pickled environment... done
[AutoAPI] Reading files... [100%] /home/juanlu/Projects/Other/sphinx-autoapi-debug/src/testpkg/__init__.py                                                                                                                                    
[AutoAPI] Mapping Data... [100%] /home/juanlu/Projects/Other/sphinx-autoapi-debug/src/testpkg/__init__.py                                                                                                                                     
[AutoAPI] Rendering Data... [100%] testpkg

[autosummary] generating autosummary for: autoapi/index.rst, autoapi/testpkg/index.rst, index.rst
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 2 source files that are out of date
updating environment: 0 added, 2 changed, 0 removed
reading sources... [100%] autoapi/testpkg/index                                                                                                                                                                                               
/home/juanlu/Projects/Other/sphinx-autoapi-debug/docs/source/autoapi/testpkg/index.rst:38: WARNING: duplicate object description of testpkg.A, other instance in index, use :noindex: for one of them
/home/juanlu/Projects/Other/sphinx-autoapi-debug/docs/source/autoapi/testpkg/index.rst:42: WARNING: duplicate object description of testpkg.A.c, other instance in index, use :noindex: for one of them
/home/juanlu/Projects/Other/sphinx-autoapi-debug/docs/source/autoapi/testpkg/index.rst:47: WARNING: duplicate object description of testpkg.A.a, other instance in index, use :noindex: for one of them
/home/juanlu/Projects/Other/sphinx-autoapi-debug/docs/source/autoapi/testpkg/index.rst:53: WARNING: duplicate object description of testpkg.A.b, other instance in index, use :noindex: for one of them