Add .. versionadded:: directives when modifying APIs

[jni]

📚 Documentation

The versionadded directive is a really nice way to tell users when particular arguments or functions were added to an API (example here). We haven't been using them in napari, which leads to some confusion about when particular APIs were added (who has time to read through a bunch of release notes?) and therefore what the minimum version of napari is to be able to use those APIs (ex: BiAPoL/napari-clusters-plotter#308 (comment)).