M3 Expressive: Button groups #184936

Button groups are a new component in M3E designed to group related buttons together, offering two main visual styles:

• Standard Button Group: This type contains multiple individual buttons. Each button within the group retains its own shape, but the group controls the spacing and arrangement.
• Connected Button Group: In this type, the buttons are visually joined, sharing borders to appear as a single, segmented unit. This style is intended to replace the existing Material 3 SegmentedButton and offers more flexibility and new styling. Connected button groups can be configured for single-selection or multi-selection.

We should create a new widget for Standard Button Group and either update SegmentedButton or create a new widget to support M3 Expressive.