In both ChangeIntPtrToSmi and ChangeInt32ToSmi we can use bitcasts
instead of change nodes for Smi Tagging, when we are using 31 bit
smis in 64 bit architectures with pointer compression enabled.

In ChangeIntPtrToSmi we can ignore the truncation as well.

Updated DecompressionOptimizer to match the new pattern.

Change-Id: I4487ba40ba9fda7b1ab31da95ff7bd144407d02d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1924355
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65168}