processor: Extract SchedEventTracker from EventTracker

Extracts ftrace/sched event related code from EventTracker into a
separate SchedEventTracker, so that we can make SchedEventTracker a
compile-time optional module later.

In preparation of aosp/1146725.

Bug: 141459049
Change-Id: I217ed56846d2fb193d803486c8df4b52b232c29c
diff --git a/Android.bp b/Android.bp
index 3380421..d42ffc9 100644
--- a/Android.bp
+++ b/Android.bp
@@ -4554,6 +4554,7 @@
     "src/trace_processor/importers/ftrace/ftrace_descriptors.cc",
     "src/trace_processor/importers/ftrace/ftrace_parser.cc",
     "src/trace_processor/importers/ftrace/ftrace_tokenizer.cc",
+    "src/trace_processor/importers/ftrace/sched_event_tracker.cc",
     "src/trace_processor/importers/fuchsia/fuchsia_provider_view.cc",
     "src/trace_processor/importers/fuchsia/fuchsia_trace_parser.cc",
     "src/trace_processor/importers/fuchsia/fuchsia_trace_tokenizer.cc",