Improve types for loader in src/browser/pages/vscode

[jsjoeio]

This is a follow-up item to #3760

Notes

Inside vscode.ts, we use (self.require as FixMeLater) = loader to add the loader. I'm not sure the proper way to type this since require is a property we're defining on self.

@code-asher also notes:

Maybe we can copy down the .d.ts for the loader to get the right type.

This might be a lot of work though, not sure. We also might need to load loader.js first and then do require.config(config) instead.

I think additional context is needed in order for this to be worked on.

Link to Loader upstream: https://github.com/microsoft/vscode-loader/blob/main/src/loader.d.ts#L280

[stale]

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