This changelist adds to the GDB stub (in class wasm::gdb_server::Target) the
logic to decode and execute GDB-remote commands and to format response packets
to be sent back to the debugger.
Here most of the commands still act as a NOOP; the actual implementation
requires interactions with the Wasm engine and will be implemented in the next
CL of this series.

Build with: v8_enable_wasm_gdb_remote_debugging = true
Run with: --wasm-gdb-remote

Bug: chromium:1010467
Change-Id: Icfa63be9e1eaa657c05876d0d4e86927e0885b90
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1938466
Commit-Queue: Paolo Severini <paolosev@microsoft.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67200}