This implements drag and drop capabilities of chat items within a `StatusChatList`.
The commit introduces a `DelegateModal` to visually reorder chat items
when they're being dragged and dropped onto a `DropArea`.
To persist the new order of chat items, various signals have been introduced to chat
list related components:
```qml
StatusChatList {
onChatItemReordered: function (id, from, to) {
// ...
}
}
StatusChatListAndCategories {
onChatItemReordered: function (categoryId, chatId, from, to) {
// ...
}
}
```
There's no such API on the `StatusChatListCategory` type because that one already
exposes its underlying `StatusChatList` via `chatList`, which makes the signal available.
Dragging and dropping chat items is disabled by default and needs to be turned on
using the `draggableItems` property:
```qml
StatusChatList {
draggableItems: true
...
}
```
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