feat(Typography): match medium font size in Sbanken theme

[snorrekim]

The css variable --font-size-medium is markedly larger in Sbanken than in DNB theme. Since this variable is mainly used for "larger" text, we have decided to make it match across themes.

• --font-size-medium now the same size in Sbanken as in DNB 1.25rem (this also fixes some unusually large text in Sbanken input components)
• added new size for Sbanken --sb-font-size-medium--plus to be used by h4 headings.

Adjustments

• <Dialog> for Sbanken now has title sizes that match Figma design
• <ProgressIndicator> for Sbanken countdown text slightly decreased
• .dnb-lead and .dnb-h--medium with <small> correctly adjusts to one size lower.
• Sbanken headings with <small> correctly adjusts to one size lower.