figure out how to specify duplicate names with breathe directives

[svenevs]

When functions with the same name but different signatures are present, breathe is not given enough information to disambiguate.

https://github.com/wjakob/nanogui/blob/f61c407ea4cb336aefcdd82202c6e09ff21b9e79/include/nanogui/common.h#L474-L476

and

https://github.com/wjakob/nanogui/blob/f61c407ea4cb336aefcdd82202c6e09ff21b9e79/include/nanogui/common.h#L493-L495

produce two separate nodes / reStructuredText documents, but .. doxygenfunction:: file_dialog is generated, which is incorrect and makes the docs for those members fail.