Development mode + web-installer can result in add-ons being unexpectedly broken

[Xon]

Affected version

2.2.13

If a user has enabled development mode, the web-installer for add-ons becomes a nasty footgun which can break add-ons and is deeply confusing for users and developers. The root of the issue is when development mode is enabled, _output will be partially updated it some parts of the add-on's data is touched/modified.

The web installer will deploy the new _data from the add-on zip but these new files will be completely ignored if _output exists. There is no warning, just a deeply broken add-on.

IMO; If someone upload a zip via the web installer, any existing _output folder for the add-on should be removed before the add-on installer is run. And display a warning about development being enabled.