Documentation: usage of types/interfaces defined in modules on global

## Search Terms - export from module to global - global namespace - declare as global - assign to global - globalThis ## Suggestion Documentation says that > It can be surprisingly difficult to access or declare values in the global scope, perhaps because we’re writing our code in modules... (https://devblogs.microsoft.com/typescript/announcing-typescript-3-4/#type-checking-for-globalthis) It shows an example how typed variable may be declared in the global scope. But it doesn't cover scenario when one needs to declare variable/function/namespace which use a type/interface declared in some module. I think that the documentation should clearly explain that it's not possible or show an example how to do it (if it's possible). ## Use Case One creates a function with input parameter and/or return type declared in module. She wants to make this function available on global. It's an anti-pattern in the same way as augmenting types from external modules, but as discussed here #5292 it exists in real life. One may have a well organised non-poluting-global modules-based codebase. But at some point by some reason she have to provide an interface for a global consumer. Moving all exposed interfaces and types to global and rewrite the codebase which used to consume them from modules would be ugly and painful. ## Example ```typescript import { SomeType, SomeInterface } from 'some/module'; function functionForGlobalConsumer(input: SomeType): SomeInterface { // some code... } globalThis.functionForGlobalConsumer = functionForGlobalConsumer; ``` ## Checklist My suggestion meets these guidelines: * [x] This wouldn't be a breaking change in existing TypeScript/JavaScript code * [x] This wouldn't change the runtime behavior of existing JavaScript code * [x] This could be implemented without emitting different JS based on the types of the expressions * [x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.) * [x] This feature…