[vm/compiler] Fix range analysis for IntConverter.

Before, converting a Uint32 to a Int32 would just clamp the range
to be within the possible Int32 range. However, that's not what the
IntConverterInstr represents in this case: in this case, it's just
a reinterpretation of the bits as signed instead of unsigned.

For simplicity's sake, the initial fix for this is to keep the range
[x, y] if it is 0 <= x <= y <= kMaxInt32, and otherwise just use
the full Int32 range.

Also add a version of Range::Full that takes a Representation instead
of a RangeSize, so that the ranges for unsigned unboxed ints can be
made more precise. Previously, they'd be overapproximated by the next
largest signed representation instead.

Also check that we're never trying to create a range for x->untagged,
and that untagged->x just uses the full range for x.

TEST=vm/dart/regress_306327173_il_test

Fixes: b/306327173

Cq-Include-Trybots: luci.dart.try:vm-aot-linux-debug-simarm_x64-try,vm-aot-linux-release-x64-try,vm-aot-linux-debug-x64-try,vm-aot-linux-debug-x64c-try
Change-Id: Ic60d24be016844deda56ee477a6950a315b8506f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/332040
Commit-Queue: Tess Strickland <sstrickl@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>