ExpansionPanel and ExpansionPanelList controls

[ndonkoHenri]

Close #1718

Test Code:

import flet as ft


def main(page: ft.Page):
    page.theme_mode = ft.ThemeMode.LIGHT

    def handle_change(e: ft.ControlEvent):
        index = int(e.data)
        panel.controls[index].is_expanded = not panel.controls[index].is_expanded
        page.update()

    def handle_delete(e: ft.ControlEvent):
        panel.controls.remove(e.control.data)
        page.update()

    panel = ft.ExpansionPanelList(
        expand_icon_color=ft.colors.AMBER,
        elevation=8,
        divider_color=ft.colors.AMBER,
        on_change=handle_change,
        controls=[
            ft.ExpansionPanel(
                bgcolor=ft.colors.BLUE_400,
                is_expanded=True,
            ),
        ],
    )

    colors = [
        ft.colors.GREEN_500,
        ft.colors.BLUE_800,
        ft.colors.RED_800,
    ]
    
    for i in range(3):
        exp = ft.ExpansionPanel(
            bgcolor=colors[i % len(colors)],
            header=ft.ListTile(title=ft.Text(f"Panel {i}")),
        )

        exp.content = ft.ListTile(
            title=ft.Text(f"This is in Panel {i}"),
            subtitle=ft.Text(f"Press the icon to delete panel {i}"),
            trailing=ft.IconButton(ft.icons.DELETE, on_click=handle_delete, data=exp),
        )

        panel.controls.append(exp)

    page.add(panel)


ft.app(target=main)