[workspace] Patch googlebenchmark to avoid shadow warnings

[jwnimmer-tri]

This allows us to remove copy-pasta in every benchmark we write.

+@rpoyner-tri for feature review, please.

\CC @RussTedrake whichever #19771 or this merges first, the other one should rebase to delete the pasta in the new benchmark, too.

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This change is 

[RussTedrake]

+@RussTedrake for feature review, if you like?

Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status: 1 unresolved discussion, LGTM missing from assignee rpoyner-tri(platform)

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systems/benchmarking/multilayer_perceptron_benchmark.cc line 27 at r1 (raw file):

  }

  void SetUp(benchmark::State& state) {  // NOLINT(runtime/references)

btw -- apparently switching to BenchmarkStateRef is another approach (used above) to trick the linter? Perhaps we should make them consistent?

[jwnimmer-tri]

Thanks @RussTedrake; I'll count you as platform review. I'd still like Rico to feature-review as our subject matter expert.

Reviewable status: LGTM missing from assignee rpoyner-tri(platform)

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systems/benchmarking/multilayer_perceptron_benchmark.cc line 27 at r1 (raw file):

Previously, RussTedrake (Russ Tedrake) wrote…

btw -- apparently switching to BenchmarkStateRef is another approach (used above) to trick the linter? Perhaps we should make them consistent?

Done

[RussTedrake]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: LGTM missing from assignee rpoyner-tri(platform)

[rpoyner-tri]

Reviewed 7 of 8 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all discussions resolved, LGTM from assignees rpoyner-tri(platform),RussTedrake(platform)