[Security Solution][EUI visual refresh] remove JSON tokens in favor of color tokens

[PhilippeOberti]

Context

Changes are made to EUI that will be visible to end-users in Kibana:

• Updated all colors in EUI
• Reduce the topmost font weights and sizes (think titles and headings)
  These changes are available in a new theme called Borealis.

See parent ticket for how to use the new theme and labels to add to the PR for tracking

Description

All usages of JSON tokens have been removed in favor of color tokens, where possible.

Exported legacy JSON tokens will be deprecated in the future and will eventually be replaced with tokens from the EUI theme. We'd appreciate it if teams could spend some time migrating away from these.

Please discontinue use of these and replace them with a JS variable from our theme context.

JSON tokens are anything from:

@elastic/eui/dist/eui_theme_light.json
@elastic/eui/dist/eui_theme_dark.json
import { euiThemeVars } from '@kbn/ui-theme'

For example:
https://github.com/elastic/kibana/blob/main/packages/kbn-visualization-ui-components/components/dimension_buttons/palette_indicator.tsx#L32

Before:

import { EuiIcon, EuiCode, EuiText, useEuiTheme } from '@elastic/eui';
...
height: ${euiThemeVars.euiSizeXS} / 2;

After:

import { useEuiTheme } from '@elastic/eui'
....
const { euiTheme } = useEuiTheme();
...
height: ${euiTheme.size.xs} / 2;

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-threat-hunting (Team:Threat Hunting)

[elasticmachine]

Pinging @elastic/security-threat-hunting-investigations (Team:Threat Hunting:Investigations)