.Net MEVD: Modify ITextSearch to react to the new LINQ-based vector search filtering

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ITextSearch accepts TextSearchOptions, which currently has an optional TextSearchFilter, which relies on the legacy non-LINQ vector search filtering feature. We need to modify it to use the new search interface. @markwallace-microsoft let me know if/when you want to discuss ideas around this.

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@markwallace-microsoft just a reminder that this will need to happen at some point, not sure who's best for this...