feat: add Split Button

[adrcotfas]

• The goal is to implement the new Split Button component
• Reuse common logic from refactor(button): improve MD3 compliance and modernize content API #4928 (PR already open)
• Reuse newly introduced tokens (shape, motion, typography, color etc)
• Extract component specific tokens for easier maintenance.
• Get inspired from TextInput/TextField, Switch, Checkbox, FAB components which have gone through modernization.
• Showcase the component in the example app
• Update the documentation