RFR: CODETOOLS-7902930: JOL: Bring back GraphWalker visitors

[Martin Junghanns]

On Thu, 20 May 2021 15:32:05 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> I can share our usage pattern. We are interested in the `path` and the `size`. Maybe it helps when designing a different / faster visitor logic: https://github.com/neo4j/graph-data-science/blob/master/proc/catalog/src/main/java/org/neo4j/gds/catalog/GraphMemoryUsageProc.java#L98-L149
>
> Pinging @s1ck again!

@shipilev thanks for the review and sorry for not reacting so quickly ��

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PR: https://git.openjdk.java.net/jol/pull/15