Fixed OfTypes case for ObjectListFilter and implemented new tests for OfTypes filter (fsprojects#522)

* Fixed `OfTypes` case for `ObjectListFilter` and implemented new tests for `OfTypes` filter with different types quantity
* Format MiddlewareTests.fs

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Co-authored-by: Viktor Tochonov <[email protected]>

Author: VectorTetra

src/FSharp.Data.GraphQL.Server.Middleware/ObjectListFilter.fs

@@ -224,7 +224,7 @@ module ObjectListFilter =
         | OfTypes types ->
             types
             |> Seq.map (fun t -> buildTypeDiscriminatorCheck param t)
-            |> Seq.reduce (fun acc expr -> Expression.Or (acc, expr))
+            |> Seq.reduce (fun acc expr -> Expression.OrElse (acc, expr))
         | FilterField f ->
             let paramExpr = Expression.PropertyOrField (param, f.FieldName)
             buildFilterExpr (SourceExpression paramExpr) buildTypeDiscriminatorCheck f.Value