use export instead of the Javascript way

[Tei1988]

Hi,
I sent PR again.
I'm happy if you review this.

The error I met

In the case using TypeScript as a esbuild configuration language, an imported GasPlugin could not be resolved its type as Plugin.

import * as esbuild from 'esbuild'
import { GasPlugin } from 'esbuild-gas-plugin'

esbuild.build({
    entryPoints: ['src/main.ts'],
    bundle: true,
    outfile: 'dist/Code.gs',  
    plugins: [GasPlugin]
})

This code made an error like below:

% npm run build                 

> src@1.0.0 build
> ts-node ./esbuild.ts

/src/node_modules/ts-node/src/index.ts:820
    return new TSError(diagnosticText, diagnosticCodes);
           ^
TSError: ⨯ Unable to compile TypeScript:
esbuild.ts:2:10 - error TS2305: Module '"esbuild-gas-plugin"' has no exported member 'GasPlugin'.

2 import { GasPlugin } from 'esbuild-gas-plugin'
           ~~~~~~~~~

    at createTSError (/src/node_modules/ts-node/src/index.ts:820:12)
    at reportTSError (/src/node_modules/ts-node/src/index.ts:824:19)
    at getOutput (/src/node_modules/ts-node/src/index.ts:1014:36)
    at Object.compile (/src/node_modules/ts-node/src/index.ts:1322:43)
    at Module.m._compile (/src/node_modules/ts-node/src/index.ts:1454:30)
    at Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
    at Object.require.extensions.<computed> [as .ts] (/src/node_modules/ts-node/src/index.ts:1458:12)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12) {
  diagnosticCodes: [ 2305 ]
}

Why this error occured?

I thought that tsc could not notice that GasPlugin is exported since the syntax esports.GasPlugin = GasPlugin is not for TypeScript but Javascript.

What does this PR change?

There are small changes in compiled files since I changed exports.GasPlugin = GasPlugin to export = { GasPlugin } in index.ts.

before:
dist/index.d.ts

export {}

dist/index.js

...
exports.GasPlugin = GasPlugin

after:
dist/index.d.ts

import type { Plugin } from 'esbuild';
declare const _default: {
    GasPlugin: Plugin;
};
export = _default;

dist/index.js

...

module.exports = { GasPlugin };

These changes makes be able to resolved GasPlugin as a Plugin for esbuild in TypeScript.
The usage is no changes.

import { GasPlugin } from 'esbuild-gas-plugin'

[mahaker]

Thanks for the contribution!
LGTM!

I'll release this feature.