[vm] Use codegen block order in regalloc in AOT.

Codegen block order keeps loop blocks together and reflecting that in
live ranges allows to produce better register allocation decisions.

Consider for example the loop:

    v = def();
    while (cond) {
      if (smth) { // (*)
        use(v);
        return true;
      }
    }

If block (*) is interspersed with loop blocks the register allocator
might decide to allocate it to the register in some of the loop blocks.
If the same block is "sunk" away from loop blocks - the register
allocator can clearly see that `v` does not necessarily have to live on
the register in the whole loop.

In JIT codegen block order is not topologically sorted and as such
is unsuitable for our linear scan.

TEST=ci

Cq-Include-Trybots: luci.dart.try:vm-aot-linux-debug-x64-try,vm-aot-mac-release-arm64-try,vm-aot-linux-release-x64-try
Change-Id: I0726815db998b559267949e157cd2158f5dd55f7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/358448
Commit-Queue: Slava Egorov <vegorov@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>