The find/replace overlay only stores a search input in the history when
an explicit search operation (forward/backward/all search) is performed.
In case only an incremental search (via search-as-you-type) is
performed, this input will not be added to the history. In some cases,
no explicit search is executed but the final result of a
search-as-you-type input is sufficient for the user. Since this final
result, after they finished typing, also represented a relevant search
input, it should be added to the history.

This change addresses the issue by adding a search input to the history
also when the overlay is left, i.e., the focus is moved to somewhere
else, such as the target editor or some other view.

Fixes https://github.com/eclipse-platform/eclipse.platform.ui/issues/2291