Feature Request: Export All TypeScript Definitions as Top-Level Named Exports

**Is your feature request related to a problem? Please describe.**

The `@google-cloud/resource-manager` package currently requires users to access its interfaces through deeply nested namespaces (e.g., `ResourceManager.protos.google.cloud.resourcemanager.v3.IProject`). This can be cumbersome and counterintuitive, particularly in TypeScript environments.

The current subpar solution for accessing the TypeScript interfaces looks like this:

```TypeScript
import * as ResourceManager from "@google-cloud/resource-manager";

const project: ResourceManager.protos.google.cloud.resourcemanager.v3.IProject = {
name: 'my-project-name',
projectId: 'my-project-id',
};
```

**Describe the solution you'd like**

I propose that all interfaces within the `@google-cloud/resource-manager` package (and also other packages if they have the same problem!) be exported as top-level named exports. This change would allow for more straightforward and cleaner import statements, enhancing the developer experience when working with TypeScript.

Benefits:

- Improves code readability and ease of maintenance.
- Simplifies the import process, making it more intuitive for developers.
- Aligns with TypeScript best practices, encouraging more widespread and effective use of the package.

With this change we could easily import TypeScript interfaces like so:

```TypeScript
import { Project } from "@google-cloud/resource-manager";

const project: Project = {
name: 'my-project-name',
projectId: 'my-project-id',
};
```