Allow paths without baseUrl in tsconfig.json

This feature was recently released in TypeScript 4.1. The paths feature in tsconfig.json allows you to do custom import path rewriting. For example, you can map paths matching @namespace/* to the path ./namespace/src/* relative to the tsconfig.json file. Previously using the paths feature required you to additionally specify baseUrl so that the compiler could know which directory the path aliases were supposed to be relative to.

However, specifying baseUrl has the potentially-problematic side effect of causing all import paths to be looked up relative to the baseUrl directory, which could potentially cause package paths to accidentally be redirected to non-package files. Specifying baseUrl also causes Visual Studio Code's auto-import feature to generate paths relative to the baseUrl directory instead of relative to the directory containing the current file. There is more information about the problems this causes here: microsoft/TypeScript#31869.

With TypeScript 4.1, you can now omit baseUrl when using paths. When you do this, it as if you had written "baseUrl": "." instead for the purpose of the paths feature, but the baseUrl value is not actually set and does not affect path resolution. These tsconfig.json files are now supported by esbuild.

Fix evaluation order issue with import cycles and CommonJS-style output formats (#542)

Previously entry points involved in an import cycle could cause evaluation order issues if the output format was iife or cjs instead of esm. This happened because this edge case was handled by treating the entry point file as a CommonJS file, which extracted the code into a CommonJS wrapper. Here's an example:

Input files:

// index.js
import { test } from './lib'
export function fn() { return 42 }
if (test() !== 42) throw 'failure'

// lib.js
import { fn } from './index'
export let test = fn

Previous output (problematic):

// index.js
var require_esbuild = __commonJS((exports) => {
  __export(exports, {
    fn: () => fn2
  });
  function fn2() {
    return 42;
  }
  if (test() !== 42)
    throw "failure";
});

// lib.js
var index = __toModule(require_esbuild());
var test = index.fn;
module.exports = require_esbuild();

This approach changed the evaluation order because the CommonJS wrapper conflates both binding and evaluation. Binding and evaluation need to be separated to correctly handle this edge case. This edge case is now handled by inlining what would have been the contents of the CommonJS wrapper into the entry point location itself.

Current output (fixed):

// index.js
__export(exports, {
  fn: () => fn
});

// lib.js
var test = fn;

// index.js
function fn() {
  return 42;
}
if (test() !== 42)
  throw "failure";