-  id is pub.name. name in lower case.
- use id to match sync installed extension with gallery extension
- use id to identify extension while installing and uninstalling
- Clean up
- Remove IExtensionIdentity
- Add util methods to create gallery id and local extension id

fixes #17113

related to #15558

This extracts the JS content from the webview html into its own file which is loaded using preload instead.