[sailfish-browser] Move resetHeight to the web page

Changes cherry-picked from SHA1 3f30d840 commit
of the new browser ui.

"Add find-in-page functionality"
True, it doesn't yet. Currently always false, this is just an enabled for now.

In new-browser-ui, find in page implementation uses this https://github.com/sailfishos/sailfish-browser/pull/225/files#diff-b4c089a7a23d339717a4b2d512897633R57 . It doesn't make sense to allow toolbar hiding when find in page is active as controls are in the toolbar.