Left-elide file/folders while keeping their extension visible

Summary:
Tweak behavior introduced in D19471.

BUG: 404955

Test Plan:
Before:
{F8325282}
After:
{F8325283}
{F8325284}

Reviewers: ngraham, #dolphin, elvisangelaccio, #vdg

Reviewed By: ngraham, #dolphin, elvisangelaccio, #vdg

Subscribers: kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D29794