Watchdog should not import CKEditor 5 utils as this leads to package duplication problem in integrations

[ma2ciek]

In other words, we should get rid of this line:

ckeditor5/packages/ckeditor5-watchdog/src/contextwatchdog.js

Line 12 in a127c97

import { toArray } from 'ckeditor5/src/utils';

And write the `toArray()` utility for this package independently.

The current situation leads to the package duplication problem because the watchdog is bundled in the integration library independently from the CKEditor 5 bundle.

[Reinmar]

It worked so far because we imported that function directly from its file, hence we didn't import index.js hence we didn't import EmitterMixin (imported by index.js) hence we didn't trigger the error.

[Reinmar]

toArray is a one line, let's inline it and remove this dep completely.