.Net: Introduce a LINQ filter preprocessor in MEVD

[roji]

This is a refactor-only change, with no functional changes. It extracts out all logic for identifying and processing captured variables ("parameters") out to a new FilterTranslationProcessor connectos support type in MEVD.

• Most databases don't support parameterization; for these we simply inline the captured variables. Connector translators see these as constants without ever having to know about captured variables etc.
• SQL databases do support parameterization. For these, the preprocessor transforms the captured variable (which is a complex tree construct) into a simple QueryParameterExpression, which can easily be pattern-matched in connector translator code.

This is preparatory work for #11673 (we need a centralized place to do this kind of thing).

[dmytrostruk]

I would keep everything related to connector support under single Microsoft.Extensions.VectorData.ConnectorSupport namespace to avoid namespace explosion and for better discoverability.