Add Lua API to access doc::UserData properties, e.g.
myLayer.extraData["extension id"].extensionCustomProperty or
myLayer.properties["extension id"].extensionCustomProperty
myLayer.extensionData["extension id"].extensionCustomProperty or
and probably
myLayer.userData.myProperty or
myLayer.userProperties.myProperty
EDIT Just in case the following design was proposed by @dacap but there is no final API design, we have to talk about the best options.
Related to https://github.com/aseprite/aseprite/issues/3625
Add Lua API to access doc::UserData properties, e.g.
and probably
as shortcut for