[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,
CommandObjectLogIncrement class.

Reviewed by: teemperor

Differential Revision: https://reviews.llvm.org/D76906