Transforming input fields

I find myself short of a simple way to perform reusable input field transformation.

Example:
```TypeScript
@InputType()
export class TestInput {
@Field()
name: string;
}
```

I would like to transform the name field before it reaches the resolver to do some basic transformation such as trimming and potentially throwing an error. Ideally I could use something such as `@Transform(transformFn)`.

I've tried `@UseMiddleware` but, alas, it does not work on input types.

Start by reviewing the @InputType and @Field example and the attempted @UseMiddleware approach described in the issue. Define how a proposed @Transform(transformFn) mechanism should process the name field before it reaches the resolver, including how transformation errors are reported; done means reusable input transformation works without relying on middleware for input types.

Written by the indexing model from the issue text.