Add fusefs_type for FUSE filesystems

Any FUSE filesystem will receive the 'fuse' type when mounted. It is
possible to change this behaviour by specifying the "context=" or
"fscontext=" option in mount().

Because 'fuse' has historically been used only for the emulated storage,
it also received the 'sdcard_type' attribute. Replace the 'sdcard_type'
attribute from 'fuse' with the new 'fusefs_type'. This attribute can be
attached on derived types (such as app_fusefs).

This change:
- Remove the neverallow restriction on this new type. This means any
  custom FUSE implementation can be mounted/unmounted (if the correct
  allow rule is added). See domain.te.
- Change the attribute of 'fuse' from 'sdcard_type' to 'fusefs_type'.
  See file.te.
- Modify all references to 'sdcard_type' to explicitly include 'fuse'
  for compatibility reason.

Bug: 177481425
Bug: 190804537
Test: Build and boot aosp_cf_x86_64_phone-userdebug
Change-Id: Id4e410a049f72647accd4c3cf43eaa55e94c318f
diff --git a/private/system_server.te b/private/system_server.te
index f35f9a8..d76a2a8 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -965,7 +965,7 @@
 
 # Allow statfs() on storage devices, which happens fast enough that
 # we shouldn't be killed during unsafe removal
-allow system_server sdcard_type:dir { getattr search };
+allow system_server { sdcard_type fuse }:dir { getattr search };
 
 # Traverse into expanded storage
 allow system_server mnt_expand_file:dir r_dir_perms;
@@ -1159,8 +1159,8 @@
 
 # Do not allow opening files from external storage as unsafe ejection
 # could cause the kernel to kill the system_server.
-neverallow system_server sdcard_type:dir { open read write };
-neverallow system_server sdcard_type:file rw_file_perms;
+neverallow system_server { sdcard_type fuse }:dir { open read write };
+neverallow system_server { sdcard_type fuse }:file rw_file_perms;
 
 # system server should never be operating on zygote spawned app data
 # files directly. Rather, they should always be passed via a