FAIL contrast on focused + selected .treeViewAppendageColumn element

[nchevobbe]

When a line is selected, the path to the file has a contrast of 2.9:1, which is not accessible

That's caused by the opacity: 0.6 in https://github.com/firefox-devtools/profiler/blob/61a58948db3cae712b5688e181d46784dc7497aa/src/components/shared/TreeView.css#L150-L153

I find it easier to redefine the color than setting lower opacity, as it's harder to exactly know how the different colors are going to play together

┆Issue is synchronized with this Jira Task