shell: stabilize test_shell_command target type

[tdyas]

Stabilize the test_shell_command target type.

[huonw]

Looks good other than:

• the deprecation period
• confirmation of the resolution for the outstanding item stabilize experimental_test_shell_command as test_shell_command #21982 / chroot substitution is inconsistent with experimental_test_shell_command #22014. My understanding is that doc updates here are the appropriate resolution?

Thanks for getting this ready.

[tdyas]

The chroot substitution issue is just a display issue due to the test goal's "output simplifier." The issue affects all tests and not just test_shell_command, so it should not be relevant to stabilizing test_shell_command.

[huonw]

Sweet! thanks for confirming.