Add absolute chart to benchmark details

[lqd]

This PR adds an absolute chart to the benchmark detail panel, to complement the relative chart:

• the relative chart easily shows cyclical noise, and the common magnitude seen on a given benchmark
• the absolute chart easily shows whether a change was noise and has returned to steady state, or is real and has stayed the same since the commit.

Screenshot

[Kobzol]

This is great, I like the horizontal layout and the fact that the graphs are both visible at once.

For me, they render below each other though:

[lqd]

I also reduced the graph width a bit so that both should fit in a single row consistently, which should fix the issue in your screenshot.

[Kobzol]

😅 I would just remove flex-wrap: wrap for this particular graphs wrapper div.

Also, I think that we should introduce a new API endpoint that will return all data necessary for the benchmark detail (I'll like to add some more data to it in the future), as we now make two API calls per opened row. But let's not do that in this PR, I'll do it in a follow-up.

[lqd]

Actually incredible. I pushed a nowrap, and hope it works for you because 3rd time's the charm.

[Kobzol]

Now it works, thanks! Just remove https://github.com/rust-lang/rustc-perf/compare/b873b613af29f44ab5be13466b82b765af690c8e..627d02e9a5f7d000f251f9f55f8c1dc54b3806cb#diff-813a534b1cbe87a3c3d6370efa9e279cec7c8083308f493d6dd95e12d9feab81R1, and otherwise LGTM.