Replace hard coded reference to CSS vars with imported react-tokens

[nicolethoen]

Sprinkled throughout the react code, we have hardcoded references to various CSS variables.
How that we are using versioned CSS variables, this will require ongoing maintenance unless we replace these hardcoded values with react tokens.

For example, the following code snippet from DataList/examples/DataListWidthModifiers.tsx

could be importing the CSS vars

import { global_Color_100 } from '@patternfly/react-tokens/dist/esm/global_Color_100';
import { global_BackgroundColor_100 } from '@patternfly/react-tokens/dist/esm/global_BackgroundColor_100';
import { global_BorderWidth_sm } from '@patternfly/react-tokens/dist/esm/global_BorderWidth_sm';

color: `var(${global_Color_100.name})`,
backgroundColor: `var(${global_BackgroundColor_100.name})`,
border: `var(${global_BorderWidth_sm.name}) solid`