* as a result of recent core engine changes to ignore rc, modules are responsible to set `failed` on nonzero RC if they want that behavior
* the `failed` filter currently triggers on nonzero RC, which caused the tests to false-pass
* updated tests to explicitly check both rc and failed keys, as well as using the failed filter.
* fixes#15770
* When running under the UTF-8 codepage, Powershell subprocesses will fail (eg, Start-Job, others) if the input encoding is using the default BOM preamble. This fix forces it to use no preamble in leaf_exec and win_shell, and includes tests to verify that Start-Job works.
* fixes#22441
* fixes#22655
* moves all env handling into the exec wrapper; this should work for everything but raw, which is consistent with non-Windows.
