add test for external modules

[mdouze]

Summary: External modules should work fine as plug-ins to Faiss in the following cases:

• additional objects that can be passed in as callbacks to Faiss

• functions that use faiss.swig_ptr to pass in arrays.

The swig_ptr functionality does not always work well (also depending on the platform). Therefore this diff adds a small external swig file to test that everything works smoothly on that end.

Differential Revision: D60379753

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D60379753

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D60379753

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D60379753

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D60379753

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D60379753

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D60379753

[mnorris11]

Hi @mdouze should we close this one since it is merged in https://github.com/facebookresearch/faiss/pull/3981 ?