Merge topic 'execute_process-encoding'

3898e53e82 execute_process: Document and test ENCODING default
d67519fce8 Help/command/execute_process: Improve formatting of ENCODING names
e1fc4b9b17 Tests/RunCMake/execute_process: Add test for ENCODING AUTO
56ae758bc5 Tests/RunCMake/execute_process: Improve test for ENCODING UTF-8

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !9816