Ability to pull and edit widget artifacts

[habuma]

The extension currently allows developers to download and edit APL. When downloaded, the APL goes into skill-package/response/display which is appropriate for normal display APL. But it is not suitable for widget APL, manifests, test data sources, etc. Those things should be downloaded into skill-package/dataStorePackages as described at https://developer.amazon.com/en-US/docs/alexa/alexa-presentation-language/apl-package-reference.html#apl-package-file-structure.

Although this can be down outside of VSCode using ask smapi export-package to pull the artifacts, it would be nice if the entire experience was contained within the editor as it is for APL.

The extension should enable downloading and editing (with preview) of widget content similarly to how it supports non-widget APL.