VisitClassesWithoutClassesLock isn't safe if classes move.

Which they do, so avoid by doing an array allocation.
Also, tidy member variables to the end of ClassLinker.
Remove unnecessary mutable. Tidy and fix a locks required/excluded.

Change-Id: I2404a9e7a1ea997d68ab1206f97d2a20dffbda06
(cherry picked from commit dbf3be0f)