Avoid unsorted recent_blockhashes for determinism

[ryoqun]

Problem

BinaryHeap::into_iter is not sorted, resulting in not-deterministic recent_blockhashes sysvar.

This is surprising as a part of the Rust community voiced.

From the API reference (Emphasis mine):

fn into_iter(self) -> IntoIter [src] [−]

Creates a consuming iterator, that is, one that moves each value out of the binary heap in arbitrary order. The binary heap cannot be used after calling this.

Summary of Changes

• Use a sorted iterator which is originally intended. Sadly, that API is still experimental so I cherry-picked from the rust GitHub repository.
  • As for licenses both (us, solana and they, rust) use Apache Lisence 2.0, so there should no problem in that regard.

Background

Found while working on #7892

Fixes #6663

[codecov]

Codecov Report

Merging #7918 into master will decrease coverage by <.1%.
The diff coverage is 86.9%.

@@           Coverage Diff            @@
##           master   #7918     +/-   ##
========================================
- Coverage    81.8%   81.8%   -0.1%     
========================================
  Files         241     244      +3     
  Lines       52121   52170     +49     
========================================
+ Hits        42678   42716     +38     
- Misses       9443    9454     +11

[t-nelson]

Oof! How'd I miss that... 🤔

Nice catch! This is absolutely the intention

[t-nelson]

lgtm

Pull request has been modified.