Merge topic 'autouic-source-group-fixes'

e8ddc1e2 Autogen: Fix a bug in setting the UIC source group
7f0151dc Help: Document the AUTOUIC_SOURCE_GROUP property
f6c47dd0 Help: Fix a typo in the AUTOGEN_SOURCE_GROUP help

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Alexey Edelev <alexey.edelev@qt.io>
Merge-request: !5978