JS: Update to pnpm workspaces

[joncinque]

Problem

All of the different JS packages in the SPL repo are roughly the same, and yet we maintain completely separate lockfiles for each one, forcing us to update dependencies on each one individually. It's a big waste of dev time and CI resources.

Solution

pnpm has great workspace support, making for much more understandable builds. And most importantly, we can specify the same dependencies to be used in the whole workspace, just like with cargo. This will take a few stages:

• [x] #5775
• [x] #5819
• [x] #5910
• [ ] Use repo-wide .eslintrc
• [x] Use repo-wide prettier