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/trace_processor/proto_incremental_state.h b/src/trace_processor/proto_incremental_state.h
index e407985..38f4abd 100644
--- a/src/trace_processor/proto_incremental_state.h
+++ b/src/trace_processor/proto_incremental_state.h
@@ -22,7 +22,7 @@
 #include <map>
 #include <unordered_map>
 
-#include "perfetto/base/optional.h"
+#include "perfetto/ext/base/optional.h"
 #include "perfetto/protozero/proto_decoder.h"
 #include "src/trace_processor/trace_blob_view.h"
 #include "src/trace_processor/trace_storage.h"