Tests - setup

[artus9033]

In relation with #40, this PR brings the following:

• [x] adds a CI workflow for running tests with GH Actions
• [x] adds tests coverage with istanbuljs, rollup-plugin-istanbul, nyc, jest and playwright-test-coverage
• adds tests base:
  • [x] unit tests (Jest + istanbuljs)
  • [x] integration (Jest + istanbuljs)
  • [x] end-to-end (Playwright)
• [x] coverage report merging (NYC) from all test types
• [ ] implements testing of - at least - the following (as in #40):
  • [ ] dragging on all types of charts is working on both axes
  • [ ] dragging on stacked charts is working
  • [x] dragging to min & max is working on both axes
  • [x] the callbacks are provided with the correct function arguments
  • [x] rounding of values is working correct
  • [x] dragData: false within a dataset is working as expected
  • ❌ ~~touch device support~~ probably no proper API in Playwright exists for that
• [ ] implements tests having a reasonable code coverage level
• [x] code coverage CI integrated with a cloud coverage platform for bot report comments, history & badges

[codecov-commenter]

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[codecov[bot]]

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