Summary:
D8785 introduced `QStandardPaths::PicturesLocation` as default
location for Copy/Move/Link To dialog.
This patch sets the starting folder to the current folder (where
the source image(s) resist). It also provides an easier handling
of switching off the history option in D11263.

CCBUG: 391527

Test Plan:
* Clear `LastTargetDir` config entry (e.g. remove `~/.config/gwenviewrc`)
* Start Gwenview
* Select one or more images and press {key F7} to copy
* Dialog should start in current folder

Reviewers: #gwenview, rkflx

Reviewed By: #gwenview, rkflx

Differential Revision: https://phabricator.kde.org/D11280