ign -> gz CMake, Config, and Example Files migration : gz-cmake

[methylDragon]

See: gazebo-tooling/release-tools#698

• Needs merge of ign -> gz FindXXX migration : gz-cmake #273

NOTE: THIS MUST BE REBASE MERGED!! Files were moved!

Description

Migrates IgnXXX.cmake files, examples, and configured files.

Hard-tocks

• ignition..in and ign..in files have been hard migrated since they're used internally. References to them in gz-cmake have also been migrated.

Tick-tocks

• All IgnXXX.cmake files have been migrated to Gz.

Some downstream packages use IgnPython.cmake and IgnBenchmark.cmake, symlinks have been installed for tick-tocking (though warnings cannot be emitted.)

[scpeters]

testing this branch for macOS and windows CI in gazebosim/gz-sim#1586

[scpeters]

looks like the IgnPython symlink doesn't work on windows:

• https://build.osrfoundation.org/job/ign_gazebo-pr-win/4711/

--- stderr: gz-math7
CMake Error at CMakeLists.txt:82 (include):
  include could not find requested file:

    IgnPython

[scpeters]

looks like the IgnPython symlink doesn't work on windows:

• https://build.osrfoundation.org/job/ign_gazebo-pr-win/4711/

--- stderr: gz-math7
CMake Error at CMakeLists.txt:82 (include):
  include could not find requested file:

    IgnPython

could we install a dummy IgnPython file that just includes GzPython? it could probably include a cmake warning in that file (similar to our ignition/*/config.hh files)

[methylDragon]

looks like the IgnPython symlink doesn't work on windows:

• build.osrfoundation.org/job/ign_gazebo-pr-win/4711

--- stderr: gz-math7
CMake Error at CMakeLists.txt:82 (include):
  include could not find requested file:

    IgnPython

could we install a dummy IgnPython file that just includes GzPython? it could probably include a cmake warning in that file (similar to our ignition/*/config.hh files)

I managed to fix it another way, I think I needed to add a prefix. Build is running now: