[scudo][standalone] Secondary & general other improvements

Summary:
This CL changes multiple things to improve performance (notably on
Android).We introduce a cache class for the Secondary that is taking
care of this mechanism now.

The changes:
- change the Secondary "freelist" to an array. By keeping free secondary
  blocks linked together through their headers, we were keeping a page
  per block, which isn't great. Also we know touch less pages when
  walking the new "freelist".
- fix an issue with the freelist getting full: if the pattern is an ever
  increasing size malloc then free, the freelist would fill up and
  entries would not be used. So now we empty the list if we get to many
  "full" events;
- use the global release to os interval option for the secondary: it
  was too costly to release all the time, particularly for pattern that
  are malloc(X)/free(X)/malloc(X). Now the release will only occur
  after the selected interval, when going through the deallocate path;
- allow release of the `BatchClassId` class: it is releasable, we just
  have to make sure we don't mark the batches containing batches
  pointers as free.
- change the default release interval to 1s for Android to match the
  current Bionic allocator configuration. A patch is coming up to allow
  changing it through `mallopt`.
- lower the smallest class that can be released to `PageSize/64`.

Reviewers: cferris, pcc, eugenis, morehouse, hctim

Subscribers: phosek, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D73507