There already exists a optional boolean flag 'replMode' for the
'Runtime.evaluate' command. This CL ferries the flag from the inspector
to DebugEvaluate::Global.

The existing DebugEvaluate::GlobalREPL is removed in favor of a
the REPLMOde enum to reduce code duplication.

Bug: chromium:1018158
Change-Id: Iafb43a3015b6876a02ac0db6cdfcac2cfa388862
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1881149
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64801}