On arm, the root register points into the middle of the roots array to
allow to use the full int12_t offset range. Therefore some offsets into
the root array are negative. This CL changes the liftoff assembler for
arm to allow loads from negative offsets.

On arm64, offsets can also be negative when pointer compression is
disabled.

Additionally this CL changes the signature of
LiftoffAssembler::LoadTaggedPointer from uint32_t to int32_t to allow
the LiftoffCompiler to provide negative indices.

This CL does not come with a separate test yet. However, this changes is
needed for https://crrev.com/c/2352784. Where there will also be a test.

R=thibaudm@chromium.org

Bug: v8:7581
Change-Id: I0a97a62ff8e934d45a4494adfbc74a3e1149c8c1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2359429Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69453}