[tests-only] throw an exception on uhandled exception in unit tests

[individual-it]

Description

• if there is an unhandled rejection throw an exception
  otherwise node 14 will only show a warning
  this leads to many crap tests, see Lots of warnings & errors when running unit tests #6337
• mock @files/src/composables to make the failing tests pass

Related Issue

• part of Lots of warnings & errors when running unit tests #6337
• blocked by Lots of warnings & errors when running unit tests #6337

Motivation and Context

don't allow crap tests

How Has This Been Tested?

• 🤖

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

Open tasks:

• ...

[kulmann]

Uff... good spot. Do you have an idea / a plan how to proceed from here? Skip the respective tests in this PR and fix them in separate PRs? Probably easier than keeping this open until the tests are fixed / modified / deleted / ... ?

[individual-it]

@kulmann I have today half a day to work on it, let me see how many of the actual issues I can fix

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[individual-it]

@kulmann it turned out to be an easy task after I found a place where @files/src/composables was mocked, THX to @janackermann for that good example

I've put the mock into jest.init.js, alternatively we can place it in every file where its needed and would not need jest.unmock('@files/src/composables') in [usePagination.spec.ts](https://github.com/owncloud/web/pull/6415/commits/26b826b11ec85247f4a4d45d98a3c6ac77085292#diff-04163efa678b56879e33803c560c520c412cb0dda7ac0b0e291d134b27a845d8)

So we can merge this PR, it's not blocked anymore

[kulmann]

🤩