FileLoader now accepts Promise instead of a File instance

[f1ames]

Suggested merge commit message (convention)

Fix: FileLoader now accepts Promise instead of a File instance. Closes ckeditor/ckeditor5#2839.

BREAKING CHANGE: The FileLoader.file property was changed to a getter which returns a native Promise instance instead of a File instance. The returned promise resolves to a File instance.

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Additional information

See ckeditor/ckeditor5#2839 for technical explanations what was changed.

This change also required some updates in ckeditor5-image and ckeditor5-easy-image plugins (because of a change in how loader.file works and it's async nature):

• Related ckeditor5-image PR: Tests: Adjusted tests to changes in upload plugin ckeditor5-image#258.
• Related ckeditor5-easy-image PR: Small adjustments for changes in upload plugin ckeditor5-easy-image#22.
• Related ckeditor5-adapter-ckfinder PR: Small adjustments for changes in upload plugin ckeditor5-adapter-ckfinder#13.

[coveralls]

Coverage remained the same at 100.0% when pulling 041f22b on t/87 into 6bd50dd on master.

[ma2ciek]

All new promises in API docs can have the Promise.<File> type.

[jodator]

All new promises in API docs can have the Promise.<File> type.

thanks for tip @ma2ciek

[jodator]

I'd use more of the Promise features both in tests (mocha nicely play with them) and in the code. Using Promise.resolve() will shorten the code a bit.

Also I've found some ugly stuff from the past (FileLoader constructor docs) which would be nice to clean up also.

ps.: Shouldn't we also update CKFinder Uupload adapter?

[f1ames]

ps.: Shouldn't we also update CKFinder upload adapter?

Looking at this line:

data.append( 'upload', this.loader.file );

I think we should 😄 Strangely, all unit tests are passing 🤔

[f1ames]

I have rechecked ckeditor/ckeditor5-easy-image#22 and ckeditor/ckeditor5-image#258 branches after refactor and updated adapter-ckfinder package too - ckeditor/ckeditor5-adapter-ckfinder#13.