execute_process: Document and test ENCODING default
The default was originally AUTO in commit 2ed473b3b8 (execute_process:
Add ENCODING option for Windows child process output, 2016-11-23,
v3.8.0-rc1~232^2) but was changed back to NONE by commit 07c3380a6e
(execute_process: Restore no-decoding default behavior, 2017-02-13,
v3.8.0-rc2~26^2) for CMake 3.8. Later it was accidentally changed back
to AUTO by commit b783e62533 (cmExecuteProcessCommand: Port to
cmArgumentParser, 2019-03-25, v3.15.0-rc1~270^2) in CMake 3.15 but the
documentation was not updated. Document the current default, AUTO, and
add a test case to verify it.
Issue: #26262
4 files changed
