Mark dependencies as external and revert to outputting CJS only

[evoactivity]

Bundling the prettier plugins meant we were building this plugin with versions of those prettier plugins from the latest prettier. People supplying older prettier's as a peer dep could then run into problems when those plugin implementations diverged.

Bundling all of @babel/core seems like a mistake to me.

Before marking these as external

dist/prettier-plugin-ember-template-tag.js   3,007.06 kB │ gzip: 580.70 kB
dist/prettier-plugin-ember-template-tag.cjs  3,007.10 kB │ gzip: 580.72 kB

after

dist/prettier-plugin-ember-template-tag.js   12.60 kB │ gzip: 3.51 kB
dist/prettier-plugin-ember-template-tag.cjs  12.63 kB │ gzip: 3.52 kB

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The prettier parsing plugins are CJS in certain versions, building this as esm and cjs doesn't help as prettier uses import() to load plugins, so our esm version is always loaded and then we try to import the cjs plugins through named exports, which does not work.

Fixes #417

[NullVoxPopuli]

Some context

#368 (review)

[evoactivity]

Yeah I'm a fan of bundling in general, but I think the prettier plugins were bundled by mistake rather than intentionally.
An argument could be made to still bundle babel, and if we do decide to bundle it again I would suggest we move to @babel/traverse as I think that's the only thing we're using.