[GCI] Add "copy filename" action to context menu in tabs.

BUG: 341352
FIXED-IN: 5.0.0

Test Plan: Tests passed. Action works as expected.

Reviewers: kfunk

Reviewed By: kfunk

Subscribers: kdevelop-devel

Projects: KDevelop

Differential Revision: https://phabricator.kde.org/D763