In case of conflict in i18n, keep the version of the branch "ours"
To resolve a particular conflict, "git checkout --ours path/to/file.desktop"

KConfigIniBackend relies on QLockFile which changes the content Uri and
this is bound to fail because we don't have permission. So, for these
Uris we use Android's Internal cache directory to save the .lock files.

GIT_SILENT

We were calling open(), then fopen(), then QFile::open(). This patch
removes the fopen() call that does not seem to do anything.

Now that KF requires Qt 5.15.2; this basically reverts commit 2e8742e64fc0
with some trivial changes.

NO_CHANGELOG

clang-tidy checks:
readability-isolate-declaration and readability-braces-around-statements

KF task: https://phabricator.kde.org/T14729

GIT_SILENT

The code was using a QSet (hash-based), use a std::set instead
for unicity, it gives us sorting for free.

We probably want to do the same in groupList(), but that's separate.

This is the case where we expected to see Key[$d] in the config file,
and it was somehow broken. When saving, the key was omitted, so when
reloading the kdeglobals key was present again.

Detected when trying to write a unittest for a different patch...

I had to reshuffle the unittest a bit because testThreads calls
testSimple which didn't expect that the "[AAA]" group would actually
be deleted now.