High contrast: Update tokens to enable high contrast theme

[andrew-ronaldson]

Follow up to #269 with the comments from Lucia below:

After design review, the following updates are needed to support HC in Topology:

• UPDATE - Topology edge stroke var is currently set to #707070, needs to be updated to global—border—color—on-secondary—default
• UPDATE - Node Group Border color should be updated to use new global—border—color—main—default token
• UPDATE - Node Group Border Width should use a calc in HC modes to give a border width of 4px on hover, and 5px on click/select. hover state: calc(global—border—width—extra-strong +1 ) / clicked state: calc(global—border—width—extra-strong +2 )
• Specs with examples of these updates can be found in this figma file: HC Topology adjustments

Another review should be done once the HC tokens are pulled into topology to make sure nothing was missed in design review!