Add search widget

[jphalip]

This widget is activated while doing a search (forward/backward, word search, etc.). It shows the current occurrence that you're on, as well as the total number of occurrences for the search terms. Works similarly to IntelliJ's built-in search tool.

This relies on search highlights being shown. But perhaps this is acceptable since the users who would care about this widget would also likely have highlights turned on?

If tests are expected for this, could you point me to some similar examples? I couldn't find tests, for example, for the macro widget.