[Conformance test] Stdout behavior with chained commands

[bogdang989]

If a command line tool runs echo a && echo b and stdout is specified as out.txt, the contents of out.txt should be a b
An executor might just run echo a && echo b > out.txt which is incorrect and would just add b to out.txt. A conformance test should clear this up.

[mr-c]

This will presumably require https://www.commonwl.org/v1.2/CommandLineTool.html#ShellCommandRequirement

[mr-c]

Places to review the spec wording
https://www.commonwl.org/v1.2/CommandLineTool.html#Running_a_Command
stdout from https://www.commonwl.org/v1.2/CommandLineTool.html#CommandLineTool and maybe https://www.commonwl.org/v1.2/CommandLineTool.html#stdout