[scudo][standalone] Introduce the SizeClassMap

Summary:
As with the sanitizer_common allocator, the SCM allows for efficient
mapping between sizes and size-classes, table-free.

It doesn't depart significantly from the original, except that we
allow the use of size-class 0 for other purposes (as opposed to
chunks of size 0). The Primary will use it to hold TransferBatches.

Reviewers: vitalybuka, eugenis, hctim, morehouse

Reviewed By: vitalybuka

Subscribers: srhines, mgorny, delcypher, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D61088

llvm-svn: 359199