Replace sandbox::policy::SandboxType with mojom Sandbox enum

sandbox.mojom.Sandbox can now be used as the sandbox type so we
replace it everywhere.

The guts of the change are in //sandbox/policy/sandbox_type.h where
SandboxType is now deleted, and //sandbox/policy/mojom/sandbox.mojom
where sandbox types that are not already used in mojom ServiceSandbox
attributes are added.

Some cascading changes:-

 - kService wasn't implemented on Mac (as it is equivalent to kUtility).
 As we cannot alias enum fields in mojo like we can in C++ I have added
 kService for Mac. The alternative is to define platform specific
 ServiceSandbox attributes for all kService interfaces which seems to
 put this complexity in the wrong place.
 - sandbox_type.h included a number of buildflag headers that other files
 then relied on. As sandbox_type.h is no longer needed in many places
 and no longer needs these defines, they have been introduced where
 required.
 - sandbox::mojom::Sandbox is forward declared in a couple of headers
 that are widely imported, hopefully reducing the number of times the
 mojom.h is included but not used.
 - some build deps must be modified.
 - LibAssistantService needs a sandbox to be defined even when hosted
 in process, so has kNoSandbox now when enable_cros_libassistant is
 false.

Bug: 1210301
Change-Id: I13fa4fa8cbbb3090a38806fe5532787bbdf1e2fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3213677
Reviewed-by: Charlie Reis <[email protected]>
Reviewed-by: Sean Topping <[email protected]>
Reviewed-by: Filip Gorski <[email protected]>
Reviewed-by: Derek Schuff <[email protected]>
Reviewed-by: Mark Mentovai <[email protected]>
Reviewed-by: Tao Wu <[email protected]>
Reviewed-by: Ken Rockot <[email protected]>
Reviewed-by: Will Harris <[email protected]>
Reviewed-by: Matthew Denton <[email protected]>
Reviewed-by: David Dorwin <[email protected]>
Commit-Queue: Alex Gough <[email protected]>
Cr-Commit-Position: refs/heads/main@{#934126}
diff --git a/content/gpu/gpu_main.cc b/content/gpu/gpu_main.cc
index 4f6a823..c9e8638c 100644
--- a/content/gpu/gpu_main.cc
+++ b/content/gpu/gpu_main.cc
@@ -93,6 +93,7 @@
 #include "content/gpu/gpu_sandbox_hook_linux.h"
 #include "content/public/common/sandbox_init.h"
 #include "sandbox/policy/linux/sandbox_linux.h"
+#include "sandbox/policy/sandbox_type.h"
 #endif
 
 #if defined(OS_MAC)