cmd/compile: use expandable columns in ssa.html

Display just a few columns in ssa.html, other
columns can be expanded by clicking on collapsed column.

Use sans serif font for the text, slightly smaller font size
for non program text.

Fixes #25286

Change-Id: I1094695135401602d90b97b69e42f6dda05871a2
Reviewed-on: https://go-review.googlesource.com/117275


Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>