[Polly][NewPM] Port IslAst to the new ScopPassManager

Summary: This patch ports IslAst to the new PM. The change is mostly straightforward. The only major modification required is making IslAst move-only, to correctly manage the isl resources it owns.

Reviewers: grosser, Meinersbur

Reviewed By: grosser

Subscribers: nemanjai, pollydev, llvm-commits

Tags: #polly

Differential Revision: https://reviews.llvm.org/D33422

llvm-svn: 303622