refactor: replace React.Children usage to more composition-friendly alternatives (#4989)

[matkoson]

Motivation

Several components inspect, classify, or mutate their children with React.Children + cloneElement. This makes composition hard: children must be direct, prop-mergeable elements of an expected type, so wrapping them (in a memo, a custom component, a helper) silently breaks the injected styling/spacing/behavior, and the injected props are not type-safe. The FAB Menu rewrite (#4963) addressed the same class of problem; this PR migrates the remaining offenders to typed props, context, and container-owned layout.

Approach

No child introspection. Each section component owns its own spacing/styling, cross-cutting state flows through context, and parents own layout (gap, padding, clipping) instead of cloning children. v6 alpha allows breaking changes without deprecation aliases, but user-visible output is preserved for documented usage; where a default that required child introspection is dropped, it is called out as a breaking change.

Changes

List.Accordion

• Removed the React.Children.map + cloneElement that injected paddingLeft and theme into expanded children.
• Added ListAccordionContext ({ leftIndent }). List.Item consumes it and indents its own container when it renders no left/right. Ripple/background stay full-width.
• Wrapped children now keep the indentation behavior. Output preserved for List.Item children (zero snapshot churn).

Dialog

• Removed the first-child cloneElement that injected marginTop: 24.
• The Dialog surface owns the top inset (paddingTop: 24); Dialog.Title and Dialog.Icon no longer add their own top offset. Dialog.Icon keeps a 16px bottom gap so icon-to-title spacing is preserved.

Dialog.Actions

• BREAKING CHANGE: no longer injects compact and uppercase into action buttons. Set them explicitly on each button. Inter-action spacing is now container gap.

Card

• Removed child counting, sibling displayName scanning, and the per-child cloneElement injection of index / total / siblings / borderRadiusStyles.
• The card clips inner content to its shape (overflow: hidden + combined border radius) instead of injecting corner styles into Card.Cover / Card.Title.
• BREAKING CHANGE: Card.Content now uses uniform vertical padding regardless of neighboring sections.

Card.Actions

• BREAKING CHANGE: no longer auto-assigns mode (previously outlined for the first action, contained for the rest) or compact. Set button props explicitly. Spacing is container gap.

ToggleButton.Row

• Removed positional Children.count / Children.map / cloneElement first/middle/last border injection.
• Segmented styling flows through ToggleButtonRowContext; the row is an MD3 segmented container (outline-colored background with hairline dividers and padding, clipped corners), and member ToggleButtons flatten their corners via context. Wrapped ToggleButtons compose correctly.
• Added an optional theme prop to ToggleButton.Row.

Out of scope (kept — idiomatic, not composition-hostile)

• Tooltip single-child trigger clone, Chip avatar-prop clone, TouchableRipple / TouchableRipple.native Children.only validation.

Deferred (follow-up PR)

• Appbar + Appbar/utils still use child counting, displayName filtering, action splitting, and cloneElement injection. Targeted for a separate change (context + explicit author ordering).

Breaking changes (summary)

BREAKING CHANGE: Card.Actions no longer injects mode/compact — pass mode="outlined"/mode="contained" (and compact if needed) explicitly.
BREAKING CHANGE: Dialog.Actions no longer injects compact/uppercase — set them explicitly.
BREAKING CHANGE: Card.Content uses uniform vertical padding regardless of neighbors.
BREAKING CHANGE: ToggleButton.Row segmented styling is reworked to an MD3 container (visual refresh).

Example migration (Card.Actions):

// before
<Card.Actions>
  <Button>Cancel</Button>
  <Button>Ok</Button>
</Card.Actions>

// after
<Card.Actions>
  <Button mode="outlined">Cancel</Button>
  <Button mode="contained">Ok</Button>
</Card.Actions>

Test plan

• yarn typecheck — pass
• yarn lint — pass (one pre-existing, unrelated TextInput warning)
• Scoped unit tests pass, with new characterization tests:
  • yarn test ListAccordion (12) — indent applied/not-applied via context
  • yarn test Dialog (12) — surface top spacing for title/content/icon-first, icon-to-title spacing, no action-prop injection
  • yarn test Card scoped (20) — clip to card shape, uniform Card.Content padding, no Card.Actions prop injection
  • yarn test ToggleButton scoped (7) — segmented styling via context
• The full yarn test suite has pre-existing animation/native-view baseline failures unrelated to this change (identical set on main); scoped runs are green.
• Manual visual inspection, before (main) vs after, on iOS (iPhone 16 Pro) and Android (Pixel 9 Pro XL): List.Accordion pixel-identical; Dialog icon-to-title spacing preserved; ToggleButton.Row segmented appearance preserved; Card reflects the intended uniform-padding change. No regressions.

Related: #4989
Reference: #4963