Use tsup to build project compatible with CJS and ESM, and validate in CI

[sjdemartini]

Should resolve #256.

This changes our packaging approach to using bundling via tsup, whereas to date we've only used tsc to generate separate JS files. It seems bundling (but not including external dependencies) is standard from most major packages I audited, and importantly tsup greatly simplifies how the build files are generated, ensuring CJS and ESM compatibility, in a way that was otherwise quite annoying.

This also now adds source maps, which will likely be useful for users of mui-tiptap.

Other options considered:

• Vite's library mode. tsup worked much more easily, such as excluding external dependencies by default, and building for CJS specifically rather than UMD.
• https://github.com/isaacs/tshy. Looks nice, but requires "type": "module" and "NodeNext" moduleResolution with typescript, which means all imports within mui-tiptap have to use .js extensions, etc., which is quite annoying. I'd prefer minimal churn here.
• "Hack" in Create esm dir package.json file to fix importing mui-tiptap in node.js contexts #257 that didn't seem to properly work

Some related reading:

• https://blog.isquaredsoftware.com/2023/08/esm-modernization-lessons/
• https://github.com/frehner/modern-guide-to-packaging-js-library

---

With this, npx @arethetypeswrong/cli and npx publint now show as valid (now also part of CI):

npx @arethetypeswrong/cli@0.15.4 --pack

mui-tiptap v1.9.5

Build tools:
- typescript@^5.1.6
- vite@^5.3.1
- tsup@^8.2.4

 No problems found 🌟


┌───────────────────┬──────────────┬────────────────────┐
│                   │ "mui-tiptap" │ "mui-tiptap/icons" │
├───────────────────┼──────────────┼────────────────────┤
│ node10            │ 🟢           │ 🟢                 │
├───────────────────┼──────────────┼────────────────────┤
│ node16 (from CJS) │ 🟢 (CJS)     │ 🟢 (CJS)           │
├───────────────────┼──────────────┼────────────────────┤
│ node16 (from ESM) │ 🟢 (ESM)     │ 🟢 (ESM)           │
├───────────────────┼──────────────┼────────────────────┤
│ bundler           │ 🟢           │ 🟢                 │
└───────────────────┴──────────────┴────────────────────┘

whereas the approach in #257 was not :

npx @arethetypeswrong/cli@0.15.4 --pack

mui-tiptap v1.9.5

Build tools:
- typescript@^5.1.6
- vite@^5.3.1

🎭 Import resolved to a CommonJS type declaration file, but an ESM JavaScript file. https://github.com/arethetypeswrong/arethetypeswrong.github.io/blob/main/docs/problems/FalseCJS.md


┌───────────────────┬────────────────────────┬────────────────────────┐
│                   │ "mui-tiptap"           │ "mui-tiptap/icons"     │
├───────────────────┼────────────────────────┼────────────────────────┤
│ node10            │ 🟢                     │ 🟢                     │
├───────────────────┼────────────────────────┼────────────────────────┤
│ node16 (from CJS) │ 🟢 (CJS)               │ 🟢 (CJS)               │
├───────────────────┼────────────────────────┼────────────────────────┤
│ node16 (from ESM) │ 🎭 Masquerading as CJS │ 🎭 Masquerading as CJS │
├───────────────────┼────────────────────────┼────────────────────────┤
│ bundler           │ 🟢                     │ 🟢                     │
└───────────────────┴────────────────────────┴────────────────────────┘

[sjdemartini]

oof, it turns out this breaks in a non-obvious way in consuming packages due to mui/material-ui#35233 (specifically what's described in mui/material-ui#35233). i.e., material-ui does not properly support imports of icons at their subpaths in an ESM context, same as https://stackoverflow.com/q/72008357/4543977. e.g. trying to use the ColorSwatchButton in an external package with this version of mui-tiptap gives:

Warning: React.jsx: type is invalid -- expected a string (for built-in components) or a class/function (for composite components) but got: object.

Check the render method of `ColorSwatchButton`.
    at http://localhost:9000/static/ui/node_modules/.vite/deps/mui-tiptap.js?v=924a118a:6591:25
...

Will try some workarounds.

[sjdemartini]

Superseded by #259

[sjdemartini]

Copying notes from #259 and adding more context about why this approach didn't work when I tried it: Both @mui/icons-material (mui/material-ui#35233) and lodash (lodash/lodash#5107) have problems being imported in a consuming package when using ESM. The path rewriting almost seemed to work (didn't break a downstream bundled package using Vite), but still caused problems for the original example node application https://codesandbox.io/p/devbox/pensive-volhard-hyhtls, with errors like:

Error: Cannot find module '/path/to/mui-tiptap-in-node/node_modules/@mui/icons-material/esm/FormatColorFill

If I force the @mui/icons-material imports to add a file extension via the import renaming, which per https://nodejs.org/api/esm.html#esm_mandatory_file_extensions should be necessary for any package that doesn't have an "exports" field (and @mui/icons-material does not), it breaks with a different problem:

/path/to/mui-tiptap-in-node/node_modules/@mui/icons-material/esm/FormatColorFill.js:3
import createSvgIcon from './utils/createSvgIcon';
^^^^^^

SyntaxError: Cannot use import statement outside a module

since icons-material doesn't in fact use proper ESM syntax internally. It's unclear whether this can be resolved without MUI fixing ESM on their end.