Default string formatting test to C locale, add localized run

Summary:
Using the user locale leads to random test failures, as arbitrary parts
may have been translated.

For localized debugging of the formatting functions, the test can be
run with the "--localized" option, using the current user locale. The
localized version is added to the test suite to increase code coverage,
but failures are ignored. In verbose mode, the formatted and localized
strings are shown.

Depends on D20032

Test Plan:
ctest
ctest -V -R propertyinfo
LANG=ar ./build/bin/propertyinfotest_bin --localized

Reviewers: Baloo, Frameworks, ngraham, astippich

Reviewed By: astippich

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D20033