`stripInternal` should remove the `export` keyword from declarations instead of removing them entirely

[DetachHead]

Bug Report

my use case for stripInternal is a type definition i want to share between two different files in my project, but not expose as part of the public api. since stripInternal removes the type entirely it breaks the types that use it.

🔎 Search Terms

stripInternal

🕗 Version & Regression Information

4.4.0-dev.20210803

💻 Code

foo.ts

/** @internal */
export type Foo = 1

export type Bar = Foo | 'bar'

bar.ts

import {Foo} from "./foo";

export type Baz = Foo | 'foo'

🙁 Actual behavior

foo.d.ts

export declare type Bar = Foo | 'bar'; //Foo doesn't exist, so Bar is now just an alias for any

bar.d.ts

import { Foo } from "./foo"; //Foo doesn't exist
export declare type Baz = Foo | 'foo'; //Baz is now just an alias for any

🙂 Expected behavior

perhaps the export keyword is stripped from internally defined types and they instead are duplicated wherever they are used in the declarations

foo.d.ts

type Foo = 1
export declare type Bar = Foo | 'bar';

bar.d.ts

type Foo = 1
export declare type Baz = Foo | 'foo';

[RyanCavanaugh]

https://www.typescriptlang.org/tsconfig#stripInternal (emph. mine)

Do not emit declarations for code that has an @internal annotation in its JSDoc comment. This is an internal compiler option; use at your own risk, because the compiler does not check that the result is valid. If you are searching for a tool to handle additional levels of visibility within your d.ts files, look at api-extractor.