karma to jest migration completed

[polbene95]

Closes #4107

In this PR we are migrating from Karma to Jest.

Extra changes:

• In day.jsx, month.jsx, & week.jsx PropTypes.instanceOf(Element) was changed for PropTypes.object because the first one doesn’t work on server side render making the test fail.

• In day.jsx we changed shouldFocusDay && this.dayEl.current.focus({ preventScroll: true }); for shouldFocusDay && this.dayEl.current?.focus({ preventScroll: true }); because in some test this.dayEl.current was null making the test fail.

What's missing:

• Scripts for test, test:ci & test:watch need to be updated.

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[martijnrusschen]

Looking good overall, would be good to get CI scripts running so we can have the test suite running.

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PullRequest Breakdown

Reviewable lines of change

+ 2,088
- 2,337

96% JavaScript (tests)
3% JavaScript
1% JSON
<1% Other (tests)

Generated lines of change

+ 1,862
- 693

Type of change

Feature - These changes are adding a new feature or improvement to existing code.

	1 Message
⚠️	Due to its size, this pull request will be reviewed by PullRequest staff before being sent to the reviewer network, and the team will reach out if there are any concerns. After this pull request is sent to the network, please be aware that it will likely have a longer turnaround time and require multiple passes from our reviewers.

[Zarthus]

Thanks so much for doing this!

I reviewed all the non-test files and it gets a big thumbs up from me.

I skimmed over the new tests and they look good to me as well.