Fix for incorrect recognition of Excel content

[Comandeer]

What is the purpose of this pull request?

Bug fix

Does your PR contain necessary tests?

All patches which change the editor code must include tests. You can always read more
on PR testing,
how to set the testing environment and
how to create tests
in the official CKEditor documentation.

This PR contains

• Unit tests
• Manual tests

What is the proposed changelog entry for this pull request?

* [#3586](https://github.com/ckeditor/ckeditor4/3586): Fixed: content pasted from Excel is not recognised by [Paste from Word](https://ckeditor.com/cke4/addon/pastefromword).

What changes did you make?

I've forced usage of raw clipboard data in canHandle method of PfW paste handler.

Closes #3586.

[f1ames]

Rebased onto latest master.

[f1ames]

Looks good 👍

Two minor tests issues to check:

All unit tests are passing on Safari, however manual test fails and I can see background-color is present in clipboard data:

I thought it's some known issue but I see we don't have anything reported 🤔 Ok, it looks like separate issue reported in #2609, could you confirm @Comandeer?

---

And some failing tests on Edge again, but I suppose its related to the instability we have (looks like #3539 (review)):

The problem is, these are always red for me now. Could you check how it works for you @Comandeer?

[Comandeer]

Ok, it looks like separate issue reported in #2609, could you confirm @Comandeer?

Yes, I ignored manual test in IE 8 and Safari.

Could you check how it works for you @Comandeer?

They pass for me on local machine. However on remote one they are more troublesome, yet I forced them to pass by manual refreshing the page several times. Seems like Edge has some serious issues with cache 🤔

[f1ames]

Rebased onto latest master.

[f1ames]

LGTM 👍