[LoopVectorize] Split out LoopAccessAnalysis from LoopVectorizationLegality

Move the canVectorizeMemory functionality from LoopVectorizationLegality to a
new class LoopAccessAnalysis and forward users.

Currently the collection of the symbolic stride information is kept with
LoopVectorizationLegality and it becomes an input to LoopAccessAnalysis.

NFC.  This is part of the patchset that splits out the memory dependence logic
from LoopVectorizationLegality into a new class LoopAccessAnalysis.
LoopAccessAnalysis will be used by the new Loop Distribution pass.

llvm-svn: 227751