Fix Token program ESM exports

[jordaaash]

This is the second of two PRs to address #3502, this one for the Token program JS (#3507 for Memo, which it builds on top of). This fixes the issues that build systems have with .mjs files by exporting .js files. It also restructures the project to be similar to Wallet Adapter / the TypeScript monorepo template I've been using.

Fixes #3502

[joncinque]

Just the one question, but otherwise looks good. Also, the node runner for the GitHub action needs to be updated to version 16

[jordaaash]

Also, the node runner for the GitHub action needs to be updated to version 16

Done, thanks! Running now.

Pull request has been modified.

[jordaaash]

Published in @solana/spl-token@0.3.2

[raymondfeng]

This change is breaking TypeScript node.js import of @solana/spl-token:

✖ ERROR: Error [ERR_REQUIRE_ESM]: require() of ES Module node_modules/@solana/spl-token/lib/cjs/index.js from solana.client.js not supported.
index.js is treated as an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which declares all .js files in that package scope as ES modules.
Instead rename index.js to end in .cjs, change the requiring code to use dynamic import() which is available in all CommonJS modules, or change "type": "module" to "type": "commonjs" in node_modules/@solana/spl-token/package.json to treat all .js files as CommonJS (using .mjs for all ES modules instead).

[jordaaash]

@raymondfeng I'm not sure what solana.client.js is or where this error is coming from. Can you open a new issue with details on how to reproduce the issue?

[raymondfeng]

@jordansexton See #3522. Thank you for the prompt response.