feat(upload)!: replace element properties

[ph-fritsche]

BREAKING CHANGE: init parameter has been removed from userEvent.upload.

What:

1. Replace properties on <input type="file"/> when changing it per userEvent.upload.
2. Remove init parameter.

Why:

The previous implementation changed the element.files properties through fireEvent and event.target.files.
That assigns the given property to the element.
As a result the element's value, type and files properties don't interact with each other any more like they do in the browser.

The init parameter has been removed for MouseEvent and there is no good reason to keep it here. See #784

How:

We can not programmatically create a FileList.
The browser creates these from trusted events and both the browser and Jsdom prevent constructing it and also prevent calling the FileList prototype methods on an object which was not created by their internal mechanism.
They also prevent setting element.files to a value that is not a real FileList.

This PR therefore introduces a utility that, given one of our FileList stubs, replaces the relevant property descriptors on the element and mimicks the browser behavior.

Checklist:

• Documentation
• Tests
• Ready to be merged

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[codecov]

Codecov Report

Merging #794 (f3e6228) into alpha (df75e5f) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             alpha      #794   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           76        77    +1     
  Lines         1547      1568   +21     
  Branches       572       576    +4     
=========================================
+ Hits          1547      1568   +21     

Impacted Files	Coverage Δ
src/setup/directApi.ts	100.00% <100.00%> (ø)
src/utility/upload.ts	100.00% <100.00%> (ø)
src/utils/dataTransfer/FileList.ts	100.00% <100.00%> (ø)
src/utils/edit/setFiles.ts	100.00% <100.00%> (ø)

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[github-actions]

🎉 This PR is included in version 14.0.0-alpha.17 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

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