cmd/bench: update gopls benchmarks to filter to -short

This fixes a breakage due to renaming of BenchmarkGoToDefinition, and
provides a means for us to configure the benchmarks run by x/benchmark
in the future.

Also add some documentation, and refactor somewhat. Remove -v for gopls
benchmarks, as that prints noisy results.

Fixes golang/go#58875

Change-Id: I862ace4af029b8042d50467567bf314b2e5521ae
TryBot-Result: Gopher Robot <>
Run-TryBot: Robert Findley <>
Auto-Submit: Robert Findley <>
Reviewed-by: Michael Pratt <>
2 files changed