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/service/BUILD.gn b/src/traced/service/BUILD.gn
index f351f0e..e19801a 100644
--- a/src/traced/service/BUILD.gn
+++ b/src/traced/service/BUILD.gn
@@ -14,7 +14,7 @@
 
 source_set("service") {
   public_deps = [
-    "../../../include/perfetto/traced",
+    "../../../include/perfetto/ext/traced",
   ]
   deps = [
     "../../../gn:default_deps",