Display header as one row in GridLayoutMnager

I am trying to show header as one row in Paging3 library using GridLayoutManager. For the footer as one row, I made following implementation :

```
val header = LoadStateAdapter { showAdapter.retry() }
binding.list.apply {
val layoutManager = layoutManager as GridLayoutManager
layoutManager.spanSizeLookup = object : SpanSizeLookup() {
override fun getSpanSize(position: Int): Int {
return if (showAdapter.getItemViewType(position) == ShowAdapter.LOADING_ITEM)
1 else layoutManager.spanCount
}
}
adapter = showAdapter.withLoadStateHeaderAndFooter(
header = header,
footer = LoadStateAdapter { showAdapter.retry() }
)
}
```

And in the Adapter, I have following implementation :

```
override fun getItemViewType(position: Int): Int {
return if (position == itemCount) SHOW_ITEM else LOADING_ITEM
}
```

How about header? How can I display it in one row?

Start with the GridLayoutManager SpanSizeLookup and the adapter getItemViewType implementation shown in the issue, then trace how withLoadStateHeaderAndFooter positions the header and footer. The work is done when the header and footer each occupy the full GridLayoutManager span count without disrupting item placement.

Written by the indexing model from the issue text.