Move UnwindTable from ObjectFile to Module

Summary:
This is a preparatory step to enable adding extra unwind strategies by
symbol file plugins. This has been discussed on the lldb-dev mailing
list: <http://lists.llvm.org/pipermail/lldb-dev/2019-February/014703.html>.

Reviewers: jasonmolenda, clayborg, espindola

Subscribers: lemo, emaste, lldb-commits, arichardson

Differential Revision: https://reviews.llvm.org/D58129

llvm-svn: 354033