processor: Refactor TrackEventParser

Makes the whole thing a bit more modular, by introducing a helper class
that contains the parsing state for a single event and splitting out
more code into methods.

Bug: 130786981, 150838542
Change-Id: I9739c969c37173ac04aa74783e9e1b0b0c5000cc
diff --git a/BUILD b/BUILD
index 64b7160..7a4eee8 100644
--- a/BUILD
+++ b/BUILD
@@ -997,6 +997,7 @@
         "src/trace_processor/slice_tracker.h",
         "src/trace_processor/stack_profile_tracker.cc",
         "src/trace_processor/stack_profile_tracker.h",
+        "src/trace_processor/status_macros.h",
         "src/trace_processor/syscall_tracker.h",
         "src/trace_processor/timestamped_trace_piece.h",
         "src/trace_processor/trace_blob_view.h",