SearchBar - Show number of matches found on page search

Summary: BUG: 395429

Test Plan: Open searchbar on webpage and type some text which is present on the page

Reviewers: #falkon, drosca

Reviewed By: #falkon, drosca

Subscribers: drosca, falkon

Tags: #falkon

Differential Revision: https://phabricator.kde.org/D27095