TrackEvent: Add support for arguments

This patch adds a way for client library users to inject custom arguments
into track events. The library still takes care of writing common track
event properties such as categories and titles; this new hook gives a way
to add add more arguments on top.

Example usage:

  TRACE_EVENT_BEGIN("category", "Title", [](perfetto::TrackEventContext ctx) {
    auto log = ctx->track_event()->set_log_message();
    log->set_body_iid(...);
  });

An upcoming patch will add a way to use interning with custom arguments like
these.

Bug: 132678367
Change-Id: Idb62d160647d037c3a2329c98d418fb53303ec65
diff --git a/Android.bp b/Android.bp
index e42c857..64f1ac3 100644
--- a/Android.bp
+++ b/Android.bp
@@ -4980,6 +4980,7 @@
     "src/tracing/platform.cc",
     "src/tracing/tracing.cc",
     "src/tracing/track_event_category_registry.cc",
+    "src/tracing/track_event_context.cc",
     "src/tracing/virtual_destructors.cc",
   ],
 }