extraPlugins configuration option should allow whitespaces between values

[arist0tl3]

Feature Request

After pulling my hair out trying to debug why I could only add one external plugin at a time, I realized that the config option extraPlugins doesn't accept whitespace between values.

Not a huge deal, but no other config options seem to have that requirement, and there is no documentation around this required format.

I feel like this is confusing, as removePlugins is fine with whitespace, but extraPlugins isnt:

Accepting whitespace would be the better solution, but a note in the docs would be the quicker one, I'm assuming.

Happy to open a PR to trim the whitespace.

[f1ames]

Thanks for reporting @arist0tl3! I can confirm it works this way and it will be good to keep removePlugins and extraPlugins settings consistent (so they both handle whitespaces).

If you feel like creating a PR, it would be great (you may want to check contributing guide)!

Btw. the code responsible for this behaviour should be probably somewhere here:
https://github.com/ckeditor/ckeditor-dev/blob/53ac710582ff47dd63ec4368cfd752db5bee6e28/core/editor.js#L499-L505

[Comandeer]

There is also third, very similar option to extraPlugins and removePlugins – plugins. The whole handling logic for these three options is in one place, so I'd broaden the scope of issue and fix also whitespaces in plugins option.

[Comandeer]

Closed in #1762.