This reduces small tagged integers on 64 bit platforms from 63 bits to
31 bits plus one tag bit.
This is a step on the way to compile-time-optional compressed pointers
on 64 bit platforms. See more about this at go/dartvmlearnings
This causes a slowdown for some uses of integers that don't fit in 31
signed bits, but because both x64 and ARM64 have unboxed 64 bit
integers now the performance hit should not be too bad.
This is a reapplication of
https://dart-review.googlesource.com/c/sdk/+/46244
It was reverted due to a compilation error on 32 bit
ARM with DBC.
R=vegorov@google.com
Change-Id: I943de1768519457f0e5a61ef0b4ef204b6a53281
Reviewed-on: https://dart-review.googlesource.com/51321
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Erik Corry
cf78da8a48