[material-next] Improve typography handling

[DiegoAndai]

Implement improvements on how we deal with typography in material next:

• Rename family to font in typescales for consistency with Material You specification
• Move pxToRem to typescale
• Create utilities for line-height calculation and letter-spacing calculation, maybe adapt createTypography
• Round letter-spacing calculation (point 1. in [LoadingButton] Fix HTML rule button > div forbidden nesting #38584 (comment))
• Use em instead of rem when applicable (letter-spacing, line-height, point 2. in [LoadingButton] Fix HTML rule button > div forbidden nesting #38584 (comment))
• Rename lineHeight to lineHeightPx in typescale, add a calculated unitless lineHeight (Suggested here)

[mj12albert]

Let's sync the typescale with the latest spec first ~ I notice it hasn't been updated for a while (since the theme structure POC!) and there are some values that are missing

[mj12albert]

Let's sync the typescale with the latest spec first ~ I notice it hasn't been updated for a while (since the theme structure POC!) and there are some values that are missing

#39514 !