Support for high contrast tokens

[mcoker]

We need to:

• Update exporter to support high contrast tokens
• Update build to parse high contrast and output to SCSS. Ideally we will have a tokens-highcontrast.scss and tokens-highcontrast-dark.scss
• Fix parsing of this value --pf-t--global--border--color--high-contrast: rgba(255, 255, 255, 0.0000)px; to remove the "px" (it's a color that's being parsed as if it's a dimension), which is parsed and saved to tokens-default.scss and tokens-dark.scss