Created Unassigned: .WhenRulePasses chainable [7155]

I'd like to be able to do:
```
RuleFor(x => x.Tenant, "Basic").NotNull().NotEmpty();
RuleFor(x => x.Tenant, "Semantic").SetValidator(new TenantValidator());
RuleFor(x => x.Foo).SetValidator(new FooValidator()).WhenRulePasses(x => x.Tenant, "Basic");
```

... so that I can make certain rules conditionally evaluate at a finer grain than #7154.