References associated with a `VarDecl` had no `RelationContainedBy` role, resulting in "orphaned" references. From the perspective of identifying unused code (in tools using the index, like [Periphery](https://github.com/peripheryapp/periphery)), this made it impossible to identify that a variable's type, initializer and custom attributes are associated with the variable.
Resolves: [SR-13766](https://bugs.swift.org/browse/SR-13766)