Decide what to do with duplicated translation contexts

[maxbarnas]

Provide a description of the task

There are 2 translation contexts with the same ID now. I missed that while reviewing and now this is on master branch.

One is in the ui package: https://github.com/ckeditor/ckeditor5/blob/1302e2b/packages/ckeditor5-ui/src/panel/balloon/contextualballoon.js#L420

The other in find-and-replace: https://github.com/ckeditor/ckeditor5/blob/1302e2b/packages/ckeditor5-find-and-replace/src/ui/findandreplaceformview.js#L479

We can either merge them and move to the core package, but then we should come up with general enough context or we can call t() with custom ID, e.g.

t( {
	string: '%0 of %1',
	id: 'Custom %0 of %1'
} )

[Reinmar]

We agreed to merge both translations and move them to core. Let's also make the context a bit more generic, e.g.:

Label for a ‘X of Y’ status of a typical next/previous navigation. For instance, ‘Page 5 of 20’.