Consistently use LoopAnalysisManager

One exception here is LoopInfo which must forward-declare it (because
the typedef is in LoopPassManager.h which depends on LoopInfo).

Also, some includes for LoopPassManager.h were needed since that file
provides the typedef.

Besides a general consistently benefit, the extra layer of indirection
allows the mechanical part of https://reviews.llvm.org/D23256 that
requires touching every transformation and analysis to be factored out
cleanly.

Thanks to David for the suggestion.

llvm-svn: 278079
diff --git a/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp b/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
index 629cb87..f6620ad 100644
--- a/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
@@ -184,7 +184,7 @@
 }
 
 PreservedAnalyses LoopInstSimplifyPass::run(Loop &L,
-                                            AnalysisManager<Loop> &AM) {
+                                            LoopAnalysisManager &AM) {
   const auto &FAM =
       AM.getResult<FunctionAnalysisManagerLoopProxy>(L).getManager();
   Function *F = L.getHeader()->getParent();