[scudo][standalone] NFC corrections

Summary:
A few corrections:
- rename `TransferBatch::MaxCached` to `getMaxCached` to conform with
  the style guide;
- move `getBlockBegin` from `Chunk::` to `Allocator::`: I believe it
  was a fallacy to have this be a `Chunk` method, as chunks'
  relationship to backend blocks are up to the frontend allocator. It
  makes more sense now, particularly with regard to the offset. Update
  the associated chunk test as the method isn't available there
  anymore;
- add a forgotten `\n` to a log string;
- for `releaseToOs`, instead of starting at `1`, start at `0` and
  `continue` on `BatchClassId`: in the end it's identical but doesn't
  assume a particular class id for batches;
- change a `CHECK` to a `reportOutOfMemory`: it's a clearer message

Reviewers: hctim, morehouse, eugenis, vitalybuka

Reviewed By: hctim

Subscribers: delcypher, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D64570

llvm-svn: 365816