keep authored line-breaks for details/type label, tweak sizing, https://github.com/microsoft/vscode/issues/99370

- merge sync state always when extension is updated
- compare version to update remote extensions with version property

- extension registers sync keys
- extension state has changed

- Implement logic to sync extension storage
- Register keys to sync provided by extension

This change:

- Make  `DocumentSelector` use a readonly array
- Updates all properties of `DocumentFilter` to be readonly

`DocumentSelector` is used as a parameter in our provider APIs and does not need to be mutable. This change lets extensions pass in readonly values for the selector

and don't create one if there are other tabs already

As it seems the desired behaviour is to just iterate through all elements, then consider using forEach or a for-of loop instead.