Minidump: Add support for the MemoryList stream

Summary:
the stream format is exactly the same as for ThreadList and ModuleList
streams, only the entry types are slightly different, so the changes in
this patch are just straight-forward applications of established
patterns.

Reviewers: amccarth, jhenderson, clayborg

Subscribers: markmentovai, lldb-commits, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61885

llvm-svn: 360908