Record-by-default creates an AppMap for a function that is run using multiprocessing

Currently, a function that's run using the multiprocessing package is instrumented, but there's no way to generate an AppMap for it. This means, for example, that the events property in the AppMap printed by mp/mp.py in https://github.com/getappmap/appmap-python/issues/200#issue-1477421807 will be empty.

appmap-python should generate multiprocessing recordings automatically, analogous to request recordings. A recording should be started before the function is run, and an AppMap created when it returns.

mp/mp.py の multiprocessing の例から始め、空のイベント出力と、issue で参照されているリクエスト記録の動作を比較します。関数がどこで計装され、記録がどこで開始および完了されるかを追跡します。関数が戻ったときに multiprocessing 関数がイベントを含む AppMap を自動的に生成すれば完了です。