LibTest/io/Process/start_A05_t01 needs to allow StateError

[sortie]

The Dart SDK change "[dart:io] Backport semantic changes from the dart:io NNBD migration."
changed the behavior of detached processes, so accessing stdout, stderr, stdin, and exitCode will throw a StateError instead of returning null.

The LibTest/io/Process/start_A05_t01 test needs to be updated to reflect this new behavior.

Additionally the test is broken except on Linux and Windows as command and args are null. The test should be changed to provide a command on all operating systems. Using Platform.resolvedExecutable unconditionally seems like the easiest solution to have an executable on all operating systems. Actually this seems to be a recurring problem in several LibTest/io/Process tests and they should all be fixed as we also run then on Mac. If the operating system is not Windows, then it's reasonable to assume basic Unix commands are available.

[sortie]

The change was reverted due to unexpected breakage. The breakage was fixed. The CL is being relanded at https://dart-review.googlesource.com/c/sdk/+/134329. However, we'll now be sending this change through the breaking change policy, so co19 shouldn't be updated until the change is relanded.

[sortie]

Breaking change request dart-lang/sdk#40483 was filed about this and the change landed in https://dart-review.googlesource.com/c/sdk/+/134329. co19 can now be updated though keep an eye on the breaking change issue for potential reverts.