Introduced select UI component

[mlewand]

Suggested merge commit message (convention)

Feature: Introduced the SelectView component. Closes ckeditor/ckeditor5#5770.

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Additional information

I didn't implement isReadOnly property as readonly is not supported on select elements in HTML so that would require workarounds.

Also I was wondering whether changing value to a value that is not contained by the select should throw an error or silently fail, doing no harm. I went with the latter, though it would be nice to log some information, but I believe we have no common mechanisms for that.

There's a subpr with manual test to this component: ckeditor/ckeditor5-theme-lark#253

[coveralls]

Coverage remained the same at 100.0% when pulling add59d8 on i/5770 into 95404e3 on master.

[oleq]

We went with a DropdownView in ckeditor/ckeditor5#1110 in this iteration to speed things up and use a component that is known to us. Whether we will use this component in the future, it's still unclear to the team and it needs to be discussed. For now, I'm unplugging it from the iteration.

[mlewand]

Closing the PR, see ckeditor/ckeditor5#5770 (comment)