Add inotify support to kernfs and anonfs.

This is consistent with Linux. Some applications recursively add
files to inotify FD. They fail if they run into kernfs files
because inotify_add_watch(2) returns EPERM in that case.

PiperOrigin-RevId: 462642204

pkg/sentry/fsimpl/devpts/devpts.go

@@ -152,6 +152,7 @@ type rootInode struct {
 	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
+	kernfs.InodeWatches
 	kernfs.OrderedChildren
 	rootInodeRefs
 

pkg/sentry/fsimpl/devpts/master.go

@@ -38,6 +38,7 @@ type masterInode struct {
 	kernfs.InodeNoopRefCount
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
+	kernfs.InodeWatches
 
 	locks vfs.FileLocks
 

pkg/sentry/fsimpl/devpts/replica.go

@@ -37,6 +37,7 @@ type replicaInode struct {
 	kernfs.InodeNoopRefCount
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
+	kernfs.InodeWatches
 
 	locks vfs.FileLocks