Port Emoji plugin to PickerPlugin handler model

[Copilot]

The emoji suggest/insert flow in roosterjs-react was still implemented as a bespoke keydown/keyup state machine. This change migrates it to the shared PickerPlugin abstraction so emoji behavior uses the same picker lifecycle and keyboard model as other pickers.

• PickerPlugin integration

  • Refactored EmojiPlugin to compose PickerPlugin(':', handler) and implement PickerHandler.
  • Delegated event processing (onPluginEvent, exclusive key handling) to PickerPlugin.

• Emoji-specific handler behavior

  • Implemented picker callbacks in EmojiPlugin:
    • onTrigger opens emoji callout and initializes query.
    • onQueryStringChanged updates emoji pane search text.
    • onSelectionChanged maps picker movement modes to EmojiPane.navigate(...).
    • onSelect commits selected emoji or expands to full picker for MoreEmoji.

• Content insertion path

  • Replaced manual selection/segment mutation with picker helper commit:
    • Build a minimal content model (Text(emoji) + SelectionMarker).
    • Commit via pickerHelper.replaceQueryString(...).
    • Close picker via helper, keeping behavior aligned with picker semantics.

this.pickerPlugin = new PickerPlugin(':', this);

public onSelect(): void {
    const selectedEmoji = this.paneRef.current?.getSelectedEmoji();
    if (selectedEmoji === MoreEmoji) {
        this.paneRef.current?.showFullPicker(this.queryString);
        return;
    }

    const model = createContentModelDocument();
    const paragraph = createParagraph();
    paragraph.segments.push(createText(selectedEmoji.codePoint), createSelectionMarker());
    model.blocks.push(paragraph);

    this.pickerHelper?.replaceQueryString(model, undefined, true);
    this.pickerHelper?.closePicker();
}

• Fixes port Emoji Plugin to use PickerPlugin #1053