[incfs] Use MountRegistry to import existing mounts on start

This is a big cleanup in IncrementalService that makes it behave
nicely on runtime restart, and more:

- fixed a bunch of threading issues in createStorage/bind
- made public functions correctly accept any path in any
  bind mount and translate it to the proper root mount
- got rid of "using namespace" in headers, cleaned includes
- removed all unused functions
- set CLOEXEC bit on all duped FDs

Bug: 151241369
Test: atest PackageManagerShellCommandTest \
  PackageManagerShellCommandIncrementalTest \
  IncrementalServiceTest

Change-Id: Ided4415aabfbfca3925b5e71c91896055886ac4a
diff --git a/services/incremental/Android.bp b/services/incremental/Android.bp
index b13d330..b8bd3b4 100644
--- a/services/incremental/Android.bp
+++ b/services/incremental/Android.bp
@@ -62,6 +62,7 @@
     srcs: [
         "incremental_service.c",
         "IncrementalService.cpp",
+        "IncrementalServiceValidation.cpp",
         "BinderIncrementalService.cpp",
         "path.cpp",
         "ServiceWrappers.cpp",