Sebastian Holtermann authored Sep 20, 2019 and Brad King committed Sep 25, 2019

We used to store information for the _autogen target in a CMake script
file AutogenInfo.cmake, which was imported by a temporary cmake instance in
the _autogen target.  This introduced the overhead of creating a temporary
cmake instance and inherited the limitations of the CMake language which
only supports lists.

This patch introduces JSON files to pass information to AUTORCC and
autogen_ targets.  JSON files are more flexible for passing data, e.g. they
support nested lists.

The patch has the side effects that

- AutogenInfo.cmake is renamed to AutogenInfo.json
- AutogenOldSettings.txt is renamed to AutogenUsed.txt
- RCC<qrcBaseName><checksum>Info.cmake is renamed to
  AutoRcc_<qrcBaseName>_<checksum>_Info.json
- RCC<qrcBaseName><checksum>.lock is renamed to
  AutoRcc_<qrcBaseName>_<checksum>_Lock.lock
- RCC<qrcBaseName><checksum>Settings.txt is renamed to
  AutoRcc_<qrcBaseName>_<checksum>_Used.txt