TrackEvent: Rename track event context for readability

This patch renames TrackEventContext and its track event accessor to
just EventContext to make trace points a little more readable.

Bug: 132678367
Change-Id: I198617c2c8ac4e4b11f7d76b01d841f328eafd50
diff --git a/Android.bp b/Android.bp
index c1be406..e305328 100644
--- a/Android.bp
+++ b/Android.bp
@@ -5042,6 +5042,7 @@
   name: "perfetto_src_tracing_client_api",
   srcs: [
     "src/tracing/data_source.cc",
+    "src/tracing/event_context.cc",
     "src/tracing/internal/in_process_tracing_backend.cc",
     "src/tracing/internal/system_tracing_backend.cc",
     "src/tracing/internal/tracing_muxer_impl.cc",
@@ -5049,7 +5050,6 @@
     "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",
   ],
 }