`importHelpers` generates code, that is incompatible with browsers

Currently enabling importHelpers adds

import * as tslib_1 from "tslib";

at the top of every source file.

Such notation is not compatible with browsers. Nowadays, all modern browsers supports Ecma modules, there's no reason for writing code that assumes Node.js environment + bundler build. Code should assume "Ecma modules" environment instead. And bundlers can stop being compilers and do the work they are supposed to do - create optimized builds (if needed at all).

The change is simple, importHelpers should generate:

import * as tslib_1 from "../../../node_modules/tslib/index.js";

The path to "node_modules" should be determined at compile time of course.

まず、importHelpers の tslib import を出力する TypeScript コンパイラコードを追跡します。現在の module specifier と、要求されたブラウザー互換のパスを比較し、次に生成された import が Ecma modules 環境から解決されること、そして node_modules のパスがコンパイル時に決定されることを確認します。