Reshuffle include/ directory layout

This CL reorganizes the include/ directory as follows:
1. The immediate subdirectories of include/ are now the stable API
   surface exposed to all embedders, with the exception of ext/.
2. ext/ contains the unstable API surface that is exposed only to chrome.

Test: builds on all configurations and passes tests
Bug: 132678367
Change-Id: If638d4b4c150fd591cd1db851283b25ff6083ed6
diff --git a/src/traced/probes/ftrace/ftrace_controller.h b/src/traced/probes/ftrace/ftrace_controller.h
index e25061d..63514b7 100644
--- a/src/traced/probes/ftrace/ftrace_controller.h
+++ b/src/traced/probes/ftrace/ftrace_controller.h
@@ -28,9 +28,9 @@
 #include <string>
 
 #include "perfetto/base/task_runner.h"
-#include "perfetto/base/utils.h"
-#include "perfetto/base/weak_ptr.h"
-#include "perfetto/tracing/core/basic_types.h"
+#include "perfetto/ext/base/utils.h"
+#include "perfetto/ext/base/weak_ptr.h"
+#include "perfetto/ext/tracing/core/basic_types.h"
 #include "src/traced/probes/ftrace/ftrace_config_utils.h"
 #include "src/traced/probes/ftrace/ftrace_thread_sync.h"