[Validation] Members should not have the same name as their enclosing type

In some languages it's a problem to have members with the same name as the enclosing type. The following declaration for instance causes the .NET generator to emit bad code: ```ts export interface Scheduler { scheduler: TransformNodeStatsDetails } ``` We should add a validation that enforces use of the `@codegen_name` tag in these kinds of situations, like e.g.: ```ts export interface Scheduler { /** @codegen_name details **/ scheduler: TransformNodeStatsDetails } ```