Move character width functions to Character class

Summary:
Replaces direct konsole_wcwidth() calls with Character object property
and the class static function, which internally still use
konsole_wcwidth().

The change also prepares the codebase for a new code for determining
character width. This way the change will barely touch existing code.

CCBUG: 396435

Test Plan:
konsole_wcwidth() is still used, just in one central place. Passed
compilation and CharacterWidthTest should be enough.

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: hindenburg, konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D15756