tracing/selftests: Update synthetic event selftest to use common_stacktrace

With the rename of the stacktrace field to common_stacktrace, update the
selftests to reflect this change. Copy the current selftest to test the
backward compatibility "stacktrace" keyword. Also the "requires" of that
test was incorrect, so it would never actually ran before. That is fixed
now.

Link: https://lore.kernel.org/linux-trace-kernel/20230523225402.55951f2f@rorschach.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>