checkboxElement in MultiSelectPanelHeaderTemplateEvent has wrong interface

[alefduarte]

Describe the bug

When customizing the panelHeaderTemplate of the MultiSelect, I encountered an issue where the checkboxElement is of type HTMLElement, which prevents me from using it directly.

I tried the following code:

const panelHeaderTemplate = (event: MultiSelectPanelHeaderTemplateEvent) => (
    <div className="p-multiselect-header" data-pc-section="header">
      {event.checkboxElement}
      {event.filterElement}
      {event.closeElement}
    </div>
);

This resulted in the error: Type 'HTMLElement' is not assignable to type 'string | number | boolean | ReactElement<any, string | JSXElementConstructor<any>> | Iterable<ReactNode> | ReactPortal | null | undefined'.

Upon reviewing the interface, I noticed that both filterElement and closeElement are of type JSX.Element, while checkboxElement is the only one designated as HTMLElement. I believe this may be a mistake, as the following workaround compiles successfully:

const panelHeaderTemplate = (event: MultiSelectPanelHeaderTemplateEvent) => (
    <div className="p-multiselect-header" data-pc-section="header">
      {event.checkboxElement as unknown as JSX.Element}
      {event.filterElement}
      {event.closeElement}
    </div>
);

Thus, I suggest that the type of checkboxElement should be changed to JSX.Element.

I will open a PR with the proposed fix.

Reproducer

https://stackblitz.com/edit/xviihaga?file=src%2FApp.tsx

System Information

System:
    OS: Windows 10 10.0.19045
    CPU: (16) x64 11th Gen Intel(R) Core(TM) i7-11850H @ 2.50GHz
    Memory: 621.42 MB / 31.67 GB
  Binaries:
    Node: 22.13.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.22 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 9.6.4 - ~\AppData\Roaming\npm\npm.CMD
    pnpm: 9.15.0 - ~\AppData\Roaming\npm\pnpm.CMD
  Browsers:
    Edge: Chromium (127.0.2651.86)
    Internet Explorer: 11.0.19041.4355

Steps to reproduce the behavior

No response

Expected behavior

No response