setConfig api option to set only in memory

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My extension dynamically generates a library bundle and sets a path in `userThirdParty` and `checkThirdParty: "ApplyInMemory"`, to allow the rest of my settings to be applied from the config.json, and library and plugin loaded, with minimal impact on the user's workspace. I currently set these two in the workspace via vscode settings apis, which leads to them being written to settings.json. Persisting these is undesirable as the `userThirdParty` path is a per-workspace path, which many users have complained about.

I noticed that the extension now provides a setConfig api, and was hoping to use this to provide those settings only in memory, but it seems they are also written back out to settings.json when set this way.

Would it be possible to have an "ApplyInMemory" option on the setConfig api for this case?

Start by tracing the setConfig API and the VS Code settings API to find where configuration changes are persisted. Done means an ApplyInMemory option applies userThirdParty and checkThirdParty without writing them to settings.json; the issue names no files or tests, so the relevant implementation and verification paths must be identified first.

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