Improve existing InputDispatcher traces

Previously, we traced using ATRACE_NAME inside an
if condition after checking if atrace was enabled. This was so that we
could avoid the addtional overhead of formatting the trace string when
there's no ongoing trace.

Since ATRACE_NAME is expected to be scoped trace of the call, doing it
inside an if condition means the scope of the trace ends immediately
once we leave the inner scope of the conditional. This essentially makes
all of our scoped traces point traces.

We get around this by adding a new helper macro ATRACE_NAME_IF that
takes a lambda that formats the message. This way, we can avoid the
formatting overhead and ensure the entire scope of the method is traced.

Bug: 210460522
Test: manual: take a trace with Perfetto
Change-Id: Ibee1e7dc5021296bdb5871dec59d8d4978fcf0c9