[6.x] Fix set picker position

[duncanmcclean]

This pull request fixes an issue where creating a Set inside Bard would cause the set picker menu to appear at the very top of the content, instead of inline where the + button was clicked.

This was happening because the Primitive component (introduced in #14290) was rendering a default wrapper element (a <span>) around the trigger slot. This extra element became the popover's trigger reference for floating-ui positioning, instead of the actual transformed trigger element (the absolute div with translateY). Since the span was at its default position (top of the editor), the popover appeared there.

This PR fixes it by adding as-child to the Primitive components, which prevents them from rendering their own DOM element and instead merges props and event handlers with the child element, preserving correct trigger positioning for floating-ui.

Fixes #14311
Caused by #14290