This CL adds a boolean flag to Runtime.evaluate that allows REPL
mode to be enabled. REPL mode hasn't landed in V8 yet, and the internal
API for it is still in flux.

R=yangguo@chromium.org

Bug: chromium:1004193
Change-Id: I281285e225d3fd2dd4175f3dd967d6562459a203
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1866510Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64470}