minor #3948 update the Sphinx extensions to raise warnings when backs…

…lashes are not ... (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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update the Sphinx extensions to raise warnings when backslashes are not ...

...escaped in namespace, class and method directives

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Commits
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1b5a300 update the Sphinx extensions to raise warnings when backslashes are not escaped in namespace, class and method directives