chore: use workspaces

[ludofischer]

• Replace deprecated prepublish with prepare https://docs.npmjs.com/cli/v7/using-npm/scripts
• Ensure packages build before testing by running the prepare script through lerna

Yarn 1 has no way to run a command in every workspace, so for now lerna is needed. I am not sure which one of the other package managers would be best at the moment.

• Updating dependencies is faster though as there is a single yarn.lock.
• When testing rush which isolates workspace dependencies, I have noticed the build script in the individual packages rely on del-cli and babel-node without declaring them in their own package.json, but I did not fix this as it seems annoying to update these dependencies in every package.

[codecov-commenter]

Codecov Report

Merging #1140 (6adb5ed) into master (a63dabf) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1140   +/-   ##
=======================================
  Coverage   96.43%   96.43%           
=======================================
  Files         116      116           
  Lines        3593     3593           
  Branches     1054     1054           
=======================================
  Hits         3465     3465           
  Misses        119      119           
  Partials        9        9           

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