Kernel/Ext2: Avoid overflow when updating UID and GID values

Previously, attempting to update an ext2 inode with a UID or GID
larger than 65535 would overflow. We now write the high bits of UIDs
and GIDs to the same place that Linux does within the `osd2` struct.

Tests/Kernel/CMakeLists.txt

@@ -40,6 +40,7 @@ serenity_test("crash.cpp" Kernel MAIN_ALREADY_DEFINED)
 set(LIBTEST_BASED_SOURCES
     TestEmptyPrivateInodeVMObject.cpp
     TestEmptySharedInodeVMObject.cpp
+    TestExt2FS.cpp
     TestInvalidUIDSet.cpp
     TestSharedInodeVMObject.cpp
     TestPosixFallocate.cpp