Migration to typescript Step 1

[Janther]

Renaming all files from js to ts makes the review process quite difficult.
In order to make the migration to typescript as easy and as clean as possible, I split it in a few steps.

important changes in this step:

• install typescript packages and add necessary configuration to build, load, and test.
• add final types
• migrated all files that git would recognise as a file renaming and not a delete x.js and create x.ts
• in the remaining js files changed the minimal amount of logic for the whole package to still work.

All tests still passing

[Janther]

Closing because ts-node has issues with node 16 and mixing esm and cjs, which our tests need.

node 18 and node 20 do work

UPDATE:
With the following changes we can make the tests run in node 16

• remove ts-node/esm from test:standalone
• only test:standalone loads the cjs files
• test:standalone only runs tests that use the built version and not the unit tests (we were already doing this in the CI for prettier V2 tests)
• load prettier directly instead of using a cjs file for non test:standalone tests