tracing/selftest: Add test to better test subops filtering of function graph

tracing/selftest: Add test to better test subops filtering of function graph

A bug was discovered that showed the accounting of the subops of the
ftrace_ops filtering was incorrect. Add a new test to better test the
filtering.

This test creates two instances, where it will add various filters to both
the set_ftrace_filter and the set_ftrace_notrace files and enable
function_graph. Then it looks into the enabled_functions file to make sure
that the filters are behaving correctly.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Andy Chiu <andybnac@gmail.com>
Link: https://lore.kernel.org/20250409152720.380778379@goodmis.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>