[Feature request] keyword `final` type for output full final type in .d.ts

<!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨 Half of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Please read the FAQ first, especially the "Common Feature Requests" section. --> ## Search Terms <!-- List of keywords you searched for before creating this issue. Write them down here so that others can find this suggestion more easily --> ## Suggestion with keyword `final`, output a final type typescript know in .d.ts ## Use Cases this help when we import `a.ts` will didn't need import other file for get type info ## Examples <!-- Show how this would be used and what the behavior would be --> > b.ts ```ts export type A2 = { a: number, } export type B2 = { b: number, } ``` ### origin > a.ts ```ts import { A2, B2 } from './b' type A1 = { a: number, } type B1 = { b: number, } export type C1 = A1 & B1 export type C2 = A2 & B2 ``` => .d.ts ```ts import { A2, B2 } from './b'; declare type A1 = { a: number; }; declare type B1 = { b: number; }; export declare type C1 = A1 & B1; export declare type C2 = A2 & B2; ``` ### with keyword `final` > a.ts ```ts import { A2, B2 } from './b' export type A1 = { a: number, } export type B1 = { b: number, } export final type C1 = A1 & B1 export final type C2 = A2 & B2 ``` => will no need to know what is A1 B1 and also will not import b.ts for know what is A2, B2 when import a.ts ```ts export declare type C1 = { a: number, b: number, } export declare type C2 = { a: number, b: number, } ``` or ```ts export declare type C1 = { a: number, } & { b: number, } export declare type C2 = { a: number, } & { b: number, } ``` ## Checklist My suggestion meets these guidelines: * [ ] This wouldn't be a breaking change in existing TypeScript/JavaScript code * [ ] This wouldn't change the runtime behavior of existing JavaScript code * [ ] This could be implemented without emitting different JS based on the types of the expressions * [ ] This isn't a runtime feature (e.g. library functio…