ANDROID: fix ABI breakage for trace_array extensions

To avoid breaking the ABI, we change trace_array_get_by_name() back to
original API and introduce the new extension API
trace_array_get_by_name_ext() and a wrapper struct trace_array_ext to
support creating instances with specified system events.

Bug: 418940629
Change-Id: I197b52af15d41b3ab56a5d94172cfa532d24ee4b
Signed-off-by: Richard Chang <richardycc@google.com>