For locales like de_AT, the current code only looks in
share/locale/de_AT/ and share/locale/de-AT/ for translation catalogs,
but not in share/locale/de/ where they most likely are.
That's because bcp47Name() returns "de-AT" for de_AT (though in the
case of de_DE e.g. it does return "de").

This patch additionally tries to fall back to the general language by
taking the part of the locale name before the first '_'.

Differential Revision: https://phabricator.kde.org/D9793

Currently the test still passed even if one of the check_translations()
calls would fail.
The reason is that check_translations() is a function which has its own
scope, so if it sets "failed" the upper level doesn't see it.

Use the PARENT_SCOPE option when setting the variable to properly
propagate the value to the upper level.

Differential Revision: https://phabricator.kde.org/D6701

Because the old implementation (accidentally) worked when you put the
ecm_create_qm_loader call in a different CMakeLists.txt file to the
target the file was added to, some projects did this.

This won't work with build-time-generated files, though, like moc files.
So we (ab)use QTimer events to make the loading happen on the main
thread.

BUG: 346188
REVIEW: 126000

Multiple ecm_create_qm_loader() with different catalog names would
overwrite each other's generated files, causing the wrong catalog to be
loaded at runtime for some targets.

This puts the catalog name into the generated filename. Since the
catalog name is the only difference between the generated files, this is
sufficient to fix the runtime behaviour.

REVIEW: 125999

This is based on commit 6745bd7e4796560959bb67e33b7c7f86f96a5a94 (and
the subsequent fix-up commits).

This broke the build for projects which used ecm_create_qm_loader in
unusual ways. A better approach is coming, but won't be in e-c-m 5.16.

This reverts commit 009c480413910e8c1a18f4d1420f4a517ea606e6.

CCBUG: 346188
CCMAIL: release-team@kde.org
CCMAIL: kde-buildsystem@kde.org

This commit is dependent on 009c480413910e8c1a18f4d1420f4a517ea606e6,
which is the primary commit to be reverted.

This reverts commit 634a0a2d3d7ba1bec2bae846acf0faf6184f4c71.