Shifting negative integrals is undefined behavior. The CL simply
switches to uint64_t when decompressing, which anyway results in
sign-extension (in standard terms, integral promotion must preserve the
value and the sign of the source operand).

The CL doesn't have any functional changes, the generated code is the
same. It only fixes the ubsan report.

Bug: chromium:1325007
Change-Id: I491a87b84d4e98b0225f76825dac2f9e85f168d1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3736442
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81452}