resources/mediawiki/mediawiki.feedback.js is a little-known built-in software feedback feature that's used by a couple of extensions, notably UploadWizard and VisualEditor.
It posts feedback to a wiki page. It used to also post user-agent information for debugging alongside the feedback. The user-agent information from posted feedback was removed in:
While the fact that user-agent information is published was disclosed, there was concern that it would be preferable to add an explicit checkbox. The following text has been vetted by legal:
On WMF sites, that would link to https://wikimediafoundation.org/wiki/Terms_of_Use - not sure we have a standard MW message that would apply here.