[GCI] Add buttons "jump to first (last) item" to standardoutputview/outputwidget.

BUG: 338153

Test Plan: Tested with cmake warnings (works fine) and c++ build errors (works fine).

Reviewers: kfunk

Reviewed By: kfunk

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D750
modified: outputview/outputmodel.cpp