Fix #472: recompose Picker collapsed value on selection change (Android)

[paulober]

A menu/automatic Picker inside a Form did not update its collapsed selected-value row when the bound value changed via the popup: the DropdownMenu checkmark moved, but the displayed row value stayed stale until the view was re-rendered for another reason (e.g. re-navigation).

The collapsed value is derived from selection.wrappedValue in processPickerContent, but a selection write through the Picker's own controls did not invalidate that Compose scope -- particularly with a bridged/@observable binding whose write happens outside Compose's snapshot system.

Add a selectionTrigger MutableState that every collapsed-value render path reads (inline, in the same Compose scope), and bump it from the menu and segmented selection actions right after writing selection.wrappedValue. That invalidates the render scope so the row re-reads the already-updated binding immediately.

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