This CL applies the following changes:
- JSCallReducer no longer generates a CheckBigInt in front of the
  generated BigIntAsUintN.
- This results in a slight change of the semantics of the latter, which
  now includes the necessary type check. Typer and Verifier are changed
  accordingly.
- The BigIntAsUintN operator is now effectful, since it can now deopt.
- IrOpcode::kBigIntAsUintN is now lowered in SimplifedLowering instead
  of EffectControlLinearizer, the necessary type check is introduced
  by the RepresentationChanger.
- Adds a small mjsunit test to check the correct deoptimization behavior
  of optimized BigInt.asUintN.
==> Remove UseInfo::TruncatingWord64()!

Drive-by: Fix an issue in ChangeUnaryToPureBinaryOp when the new_input
is at index 1.
Drive-by: Introduce an %Is64Bit() intrinsic to allow tests to
distinguish 32 and 64 bit architectures.

Bug: v8:11682
Change-Id: I448f892d3bd2280d731ae5b248c833de8faf1bd5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2843816
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74147}