Fix "Failed to load message bundle" error in remote-ssh development

[roblourens]

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In the development build, we should not include the nls webpack loader. To check the mode flag, we need to change the config to export a function instead of an object

Example:

https://github.com/microsoft/vscode-remotehub/blob/main/extensions/remotehub/webpack.config.js#L83-L94

https://webpack.js.org/configuration/mode/#mode-none