Make "Show hidden files" action follow HIG
The action is a toggle action, for which the HIG prescribes that the text should describe the action's checked state, and neither the text nor the icon should change when the action is checked. Other toggle actions in Dolphin follow these rules, but this one does not.
This commit makes the action follow those rules.
Unchecked state:
Checked state:
cc @teams/vdg