Add Kotlin (.kt) mimetype icons

Summary:
FEATURE: 401299

FIXED-IN: 5.54

Add an icon for Kotlin files (.kt).

Test Plan: {F6547502}

Reviewers: #vdg, ngraham, ndavis

Reviewed By: #vdg, ngraham, ndavis

Subscribers: alex-l, ngraham, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D18199