[WIP] Update documentation for debugging determinism

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Please update https://github.com/dotnet/roslyn/blob/main/docs/compilers/Deterministic%20Inputs.md to add more details on the debugging determinism

Some details to include:

1. Building with /p:Features="debug-determinism" to generate the key file, which can be diff'd between builds to see if the inputs to the compiler were different

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[dibarbet]

hit enter too fast