AK: Rename Time to Duration

That's what this class really is; in fact that's what the first line of
the comment says it is.

This commit does not rename the main files, since those will contain
other time-related classes in a little bit.

Kernel/FileSystem/RAMFS/Inode.cpp

@@ -381,7 +381,7 @@ ErrorOr<void> RAMFSInode::truncate(u64 size)
     return {};
 }
 
-ErrorOr<void> RAMFSInode::update_timestamps(Optional<Time> atime, Optional<Time> ctime, Optional<Time> mtime)
+ErrorOr<void> RAMFSInode::update_timestamps(Optional<Duration> atime, Optional<Duration> ctime, Optional<Duration> mtime)
 {
     MutexLocker locker(m_inode_lock);