This patch adds a variant of EmbedderGraph::AddEdge() which
allows the embedder to specify the name of an edge. The edges
added without name are element edges with auto-incremented indexes
while the edges added with names will be internal edges with
the specified names for more meaningful output in the heap
snapshot.

Refs: https://github.com/nodejs/node/pull/21741
Bug: v8:7938
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I8feefa2cf6911743e24b3b2024e0e849b0c65cd3
Reviewed-on: https://chromium-review.googlesource.com/1133299
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54412}