[WIP] Update deprecated rootUri to workspaceFolders in sample

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Deprecated rootUri is used for lsp-multi-server-sample</issue_title>
<issue_description>The example server is still using params.rootUri https://github.com/microsoft/vscode-extension-samples/blob/master/lsp-multi-server-sample/server/src/server.ts#L25

Which makes sense in the usecase, but as it says, that it's deprecated and we should use params.workspaceFolders which does not help us to figure out which workspace folder this server was started for.

So is starting a server for every workspace folder still what's recommended? https://github.com/microsoft/vscode-extension-samples/blob/master/lsp-multi-server-sample/README.md#L5

Or should we handle this different nowadays?</issue_description>

Comments on the Issue (you are @copilot in this section)

@dbaeumer This is a fair point and needs to be addressed the LSP libs. Things to do is to only send the single workspace folder to the server if it is set in the client. @dbaeumer Fix the LSP libs. Moving back to extension sample to adapt when new version is released.

• Fixes Deprecated rootUri is used for lsp-multi-server-sample #516

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