kcmshell6: Use KShell to split values coming from args option
The name suggests plural, but we'd handle the value. In kde-cli-tools kcmshell5, we would do "parser.value(QStringLiteral("args")).split(QRegularExpression(QStringLiteral(" +")))". But this would have ignored multiple --args calls.
Test Plan: Add debug output and expect all args to be part of args ./bin/kcmshell6 kcm_plasmasearch --args "bla1 bla2 bla3" --args "second1 second2" ./bin/kcmshell6 kcm_plasmasearch --args "bla1 bla2 bla3"