[MAINTENANCE]: Clean up `.npmignore` file

[emilykl]

The Plotly.js tarball published to NPM includes lots of development files that it probably shouldn't, which creates a huge bundle size.

We also had an issue recently where a large folder was included in a bundle by mistake.

We should update .npmignore such that only the required files are included in the bundle.

[camdecoster]

Let's include the following in the .npmignore file:

.vscode
.tool-versions

[camdecoster]

It's worth noting that .gitignore is ignored if .npmignore is present.