update build config, removing need for tslib dependency

[zxbodya]

Reasons for making this change

fixes #3958

Updating tsconfig files:

• "importHelpers": false to remove need for tslib dependency
• increase compilation target level from es6 to es2018 (so there are no need for transpiling object spread/rest feature, and so the helper for which tslib was needed)
• add missing typescript project reference for snapshot-tests in a root tsconfig, also update it to use es modules like other packages

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests. I've run npm run test:update to update snapshots, if needed.
  • I've updated docs if needed
  • I've updated the changelog with a description of the PR
• I'm adding a new feature
  • I've updated the playground with an example use of the feature