Deprecation warnings within the tooling

[philrz]

As our query language has evolved, we've expressed plans to deprecate some parts of it, such as how aggregate has taken the place of the former summarize operator (#5722) or proposed changes to from (#5143) and boolean operators (#4782). Our general approach is likely to keep the older approaches around before removing them entirely from the grammar, and Release Notes and docs (e.g., #5751) are one way to communicate this to users well in advance of a disruptive change. However, knowing users often don't closely follow all such materials, as a courtesy to users it might be good if we add a formal channel within the tooling itself to inform a user that some part of their query is planned to be phased out, perhaps with specific details of when it will be finally removed, in an attempt to nudge them toward changing their queries in advance.