x/benchmarks: monitor binary size

[aclements]

We should monitor binary size in the performance dashboard.

Probably this makes the most sense to report as additional metrics on the GoBuild* benchmarks, which means integrating this into Sweet. As a starting point, we can just report total binary size. It would be nice to break it out into at least text and data, but that would mostly serve to help us understand changes in binary size.

We do have a way to indicate that certain metrics have an "exact" distribution, but I'm not sure if that's wired into the dashboard analysis.

@mknyszek @prattmic @dr2chase

[qmuntal]

Given that the binary size metric is builder-agnostic (cgo aside), could we generate this metric for all first-class ports by cross-compiling from the linux-amd64-perf builder?

[prattmic]

We do have a way to indicate that certain metrics have an "exact" distribution, but I'm not sure if that's wired into the dashboard analysis.

I'm not sure if it is wired up or not, but if not we already run GoBuild benchmarks N times, so we can just report the same binary size N times which should result in low/zero variance.

[gopherbot]

Change https://go.dev/cl/462718 mentions this issue: cmd/bench: benchmark binary size and build time via bent

[gopherbot]

Change https://go.dev/cl/462956 mentions this issue: cmd/bent: log toolchain prior to compilation

[gopherbot]

Change https://go.dev/cl/462957 mentions this issue: cmd/bent: clean up benchsize