C# Analyzers: Prevent mutation of customer provided ClientOptions objects

ClientOptions instances can be reused across multiple clients so we should never mutate them.

Should catch things like:

cc @AlexanderSher @JoshLove-msft @christothes @annelo-msft

The issue names no files, tests, or analyzer entry points and includes only an example image. Start by locating the C# analyzer project and its existing mutation-detection tests; the work is done when customer-provided ClientOptions mutations are reliably reported without false positives.

Written by the indexing model from the issue text.