Iterate Colors for Rainbow Brackets

Following https://github.com/vizhub-core/vzcode/pull/708

In src/client/themes/vizhubTheme/index.ts, we can tweak the colors to match the theme more closely.

Each of these sub-points could be done as separate PRs:

[ ] Develop a set of colors for rainbow brackets that works well for dark themes, and use that for VizHub theme
[ ] Disable rainbow brackets for light themes for now
[ ] Develop a different set of colors for rainbow brackets that works well for light themes
[ ] Integrate those into the themes we're using

        '.rainbow-bracket-red > span': {
          color: 'white',
        },
        '.rainbow-bracket-orange > span': {
          color: 'violet',
        },
        '.rainbow-bracket-yellow > span': {
          color: 'deepskyblue',
        },
        '.rainbow-bracket-green > span': {
          color: 'lime',
        },
        '.rainbow-bracket-blue > span': {
          color: 'yellow',
        },
        '.rainbow-bracket-indigo > span': {
          color: 'orange',
        },
        '.rainbow-bracket-violet > span': {
          color: 'red',
        }

vizhub-core / vzcode

Iterate Colors for Rainbow Brackets #723