.Net MEVD: Consider obsoleting VectorSearchOptions.VectorPropertyName in favor of a strongly-typed lambda VectorPropertySelector

[roji]

VectorSearchOptions currently has VectorPropertyName, allowing the user to specify which vector property is to be searched (for cases where there are multiple vector properties). The property is a string representing the storage name.

However, in most (ideally all) APIs on MEVD, the interaction with the record is via strongly-typed property accesses on the user .NET type, rather than weakly-typed storage property names. For example, we're moving away from the current filter mechanism - which relies on storage string properties - to using LINQ expressions, which allow referencing .NET properties; this proposes that we do the same for selecting the vector property:

// Current API:
var results = await fixture.Collection.VectorizedSearchAsync(
    new ReadOnlyMemory<float>([1, 2, 3]),
    new() { VectorPropertyName = "some_vector_prop" });

// New API:
var results = await fixture.Collection.VectorizedSearchAsync(
    new ReadOnlyMemory<float>([1, 2, 3]),
    new() { VectorProperty = r => r.SomeVectorProp });

/cc @westey-m

[adamsitnik]

Implemented in #10850