refactor: manually write index.d.ts for now

Refs: denoland/deno#3385

Author: keithamus

index.d.ts

@@ -0,0 +1,26 @@
+interface Result {
+  name: 'AssertionError' | 'AssertionResult'
+  ok: boolean
+  toJSON(...args: unknown[]): Record<string, unknown>
+}
+
+declare class AssertionError<T> extends Error implements Result {
+  [key: string]: unknown;
+  name: 'AssertionError';
+  ok: false;
+  message: string;
+  constructor(message: string, props?: T, ssf?: Function);
+  stack: string;
+  toJSON(stack?: boolean): Record<string, unknown>;
+}
+
+declare class AssertionResult<T> implements Result {
+  [key: string]: unknown;
+  name: 'AssertionResult';
+  ok: true;
+  message: string;
+  constructor(props?: T);
+  toJSON(): Record<string, unknown>;
+}
+
+export {Result, AssertionError, AssertionResult}

mod.ts

@@ -1,12 +1,8 @@
+import {Result} from './index.d.ts'
+
 const canElideFrames = "captureStackTrace" in Error;
 const startStackFrames = new WeakMap();
 
-interface Result {
-  name: "AssertionError" | "AssertionResult";
-  ok: boolean;
-  toJSON(...args: unknown[]): Record<string, unknown>;
-}
-
 export class AssertionError<T> extends Error implements Result {
   [key: string]: unknown