The event pictureViewsGenerationDone fires twice in LTS 2021, once in LTS 2019

When uploading an image via WebUI, the `pictureViewsGenerationDone` event is fired once in LTS 2019, and twice in LTS 2021.

To reproduce:

• In your IDE set a breakpoint inside `org.nuxeo.ecm.platform.picture.recompute.RecomputeViewsAction.compute()` on the `fireEvent` call.
• Launch a Nuxeo server with WebUI installed and attach your debugger
• Login to WebUI
• Create a Workspace
• Drag and drop an image into the workspace

Notes:

While debugging I noticed that `compute()` runs with a different user each time. One call has the session of the current user. The other call has the session of the `system` user (see screenshots). The order is not consistent, in one project the user comes first, in another project system comes first.

Why is this a problem? If you have an event handler, they run in parallel so it makes any business logic pretty wonky.