Allow extension to specify storeName

[panuhorsmalahti]

If extension's package.json specifies storeName property which is set to a truthy value, use it for persisting data (e.g. extension stores and extension data) instead of the extension name.

This allows extension to be renamed without losing data.

[panuhorsmalahti]

Note that extension can set the storeName also in an injectable (using bundledExtensionInjectionToken).

[Nokel81]

It is the opinion of the core team that using a field within the package.json would be preferable.