Add null propagation/protection logic for InMemory provider.

[maumar]

When we bind to a non-nullable property on entity that can be nullable (e.g. due to left join) we modify the result to be nullable, to avoid "nullable object must have a value" errors. This nullability is then propagated further. We have few blockers:

• predicates (Where, Any, First, Count, etc): always need to be of type bool. When necessary we add "== true".
• conditional expression Test: needs to be bool, same as above
• method call arguments: we can't reliably rewrite methodcall when the arguments types change (generic methods specifically), we convert arguments back to their original types if they were changed to nullable versions.
• method call caller: if the caller was changed from non-nullable to nullable we still need to call the method with the original type, but we add null check before - caller.Method(args) -> nullable_caller == null ? null : (resultType?)caller.Method(args)
• selectors (Select, Max etc): we need to preserve the original result type, we use convert
• anonymous type, array init: we need to preserve the original type, we use convert

Also enable GearsOfWar and ComplexNavigation tests for in memory.

[smitpatel]