Consider camel casing xl and xxl tokens

[literat]

#1932

headingXlargeBold -> headingXLargeBold

Proof-of-concept solution:

/**
   * Transform the next character after `X` to uppercase.
   *
   * Example:
   * - `heading-xsmall` -> `headingXSmall`
   * - `heading-xlarge` -> `headingXLarge`
   */
  return safeName.replace(
    /(X+)([a-z])/g,
    (_match, xs: string, next: string) => `${xs.toUpperCase()}${next.toUpperCase()}`,
  );

☝ should be done more precisely and allow only certain values.