Auto install bundle

Automatically install extensions "bundled" with installer on startup.

**Issues**:
* Should appReady in ExtensionManger be used instead?
* Terminology: folder name and location

cc @dangoor @peterflynn 

This is for #9233 
`FileSystem.getDirectoryForPath(dirPath)` will return an `EntryConstructor` object, then "what @dangoor said" :)