If a breakpoint is set on a non-breakable position, the wasm interpreter
just stores the value 0xFF (kInternalBreakpoint) in the function body
(actually, a copy of the function body). This might overwrite immediates
and cause subsequent failures in the wasm interpreter.

In JavaScript, breakpoints are just forwarded to the next breakable
position. This CL implements the same for WebAssembly.
A cctest tests this behavior, and the existing
wasm-stepping-byte-offsets.js inspector test is extended to also set the
breakpoint within an i32 constant immediate.

R=leese@chromium.org, mstarzinger@chromium.org
CC=​bmeurer@chromium.org

Bug: chromium:1025184
Change-Id: Ia2706f8f1c3d686cbbe8e1e7339d9ee86247bb4a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1925152
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65070}