This implements inspection of live registers on breakpoints in Liftoff.
To that end, the frame pointer of the WasmDebugBreak frame is remembered
when iterating the stack. Based on a platform-specific implementation of
{WasmDebugBreakFrameConstants}, the offset of the respective register
within that frame is computed, and the value is read from the frame.

As a drive-by, the wasm debug side table is storing register codes as
liftoff codes, which can also store register pairs (needed for i64 on
32-bit platforms, and for SIMD, which is not supported yet).

R=jkummerow@chromium.org
CC=thibaudm@chromium.org

Bug: v8:10222
Change-Id: I01b669baf56430e100cd46cc46f210121ea679da
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2102574Reviewed-by: Simon Zünd <szuend@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66719}