Dolphin Service Menu installer cleanup

Summary:
This patch contains some smaller formatting/coding style changes
to avoid unrelated changes in other patches.

• Use {} instead of QStringList{} consistently
• Use parehthesese in UncompressCommand({}) consistently
• Use QStringList name = {} instead of auto name = QStringList{}
• Add one qAsConst, remove qAsConst if value is already const

Test Plan: Compile, install and run tests

Reviewers: Dolphin, ngraham, nicolasfella

Subscribers: kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D28801