[corlib] Harden CustomAttributeData::GetHashCode
Revert "[runtime] Don't pass SEE_MASK_NOCLOSEPROCESS to ShellExecuteEx as we don't care for the launched process. Part 1/3 of Bug #16119."

This reverts commit 6c06d109952acb28a8198dcf85a6e8f4d4393985.
[System] Fix process creation when UseShellExecute is set to false.

This fixes the behavior of process spawning when UseShellExecute is
set to true.

The right behavior is to return no process only when we used the system
launcher. So, spawning /bin/cat should behave in the same way independent
of how UseShellExecute is set.