Allow the DevTools frontend to evaluate variables in a wasm frame context by
reusing the existing Debugger expression evaluation API. Where previously the
API expected JavaScript expressions, which would in general just fail, now the
expression is expected to be base64 encoded Wasm that creates a JSON string in
linear memory.

Bug: chromium:1020120 chromium:1068571
Change-Id: I4b31fdb9d3b21b4e08c4995ec2f07880923959e9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2087396Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Philip Pfaffe <pfaffe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67568}