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/SysFS/Inode.cpp

@@ -110,7 +110,7 @@ ErrorOr<void> SysFSInode::truncate(u64 size)
     return m_associated_component->truncate(size);
 }
 
-ErrorOr<void> SysFSInode::update_timestamps(Optional<Time>, Optional<Time>, Optional<Time>)
+ErrorOr<void> SysFSInode::update_timestamps(Optional<Duration>, Optional<Duration>, Optional<Duration>)
 {
     return {};
 }