[lldb] Fixing the bug that the "log timer" has no tab completion
I fixed the bug that the "log timer" has no tab command.
Original code has the only CommandObjectLogTimer class, but it is not
sufficient. Thus I divided the content of CommandObjectLog class into
CommandObjectLogEnable class, CommandObjectLogDisable class,
CommandObjectLogDump class, CommandObjectLogReset class,
Reviewed by: teemperor
Differential Revision: https://reviews.llvm.org/D76906