Fix ESM import in core package by adding .babelrc and babel-plugin-add-import-extension

[Shellishack]

This fixes issues from #731.

Here is the codesandbox that implements this https://codesandbox.io/p/github/Shellishack/webpack-esm-sandbox/fork-fix. After adding the babel plugin, core builds for ESM contains ".js" suffix in import clauses. So webpack no longer complains things like:

ERROR in ./node_modules/@uiw/react-codemirror/esm/index.js 5:0-48
Module not found: Error: Can't resolve './useCodeMirror' in 'C:\GitHub\pulse-editor-code-view\node_modules\@uiw\react-codemirror\esm'
Did you mean 'useCodeMirror.js'?

This might be a fix only for Webpack (I am only familiar with Webpack). May need more testing for Vite, etc.

I am sure if adding a babel plugin in this case would be the most appropriate solution, since it was the building tool that did not include file extensions in imports. Is it a behavior from tsbb causing this issue? LMK what you think.

[jaywcjlove]

Thank you for your PR submission. After testing, everything works fine.

[jaywcjlove]

@Shellishack thx! I refactored the babel-plugin-add-import-extension package and integrated it into the tsbb build tool, effectively solving similar issues across all dependencies.