New sync package.

* Rename syncutil to sync.
* Add aliases to sync types.
* Replace existing usage of standard library sync package.

This will make it easier to swap out synchronization primitives. For example,
this will allow us to use primitives from github.com/sasha-s/go-deadlock to
check for lock ordering violations.

Updates #1472

PiperOrigin-RevId: 289033387

pkg/sentry/fsimpl/tmpfs/BUILD

@@ -47,6 +47,7 @@ go_library(
         "//pkg/sentry/usage",
         "//pkg/sentry/usermem",
         "//pkg/sentry/vfs",
+        "//pkg/sync",
         "//pkg/syserror",
     ],
 )

pkg/sentry/fsimpl/tmpfs/regular_file.go

@@ -17,7 +17,6 @@ package tmpfs
 import (
 	"io"
 	"math"
-	"sync"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
@@ -30,6 +29,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/usage"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 

pkg/sentry/fsimpl/tmpfs/tmpfs.go

@@ -26,7 +26,6 @@ package tmpfs
 import (
 	"fmt"
 	"math"
-	"sync"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
@@ -34,6 +33,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 )