`EditableText` drag selection fix (#24260)

# Objective

`on_pointer_drag` queues `MoveToPoint` as well as
`ExtendSelectionToPoint` when dragging. So each time the mouse moves
during a drag, the current selection is cleared and a new selection is
created. As long as the local drag start position is constant this is
seamless, but if you scroll the text input view, the start of the drag
is now at a different position relative to the text layout, and the
start of the selection range changes.

## Solution

Don't queue the `MoveToPoint` edit.

## Testing

Enter enough text to overflow the input's view, then select and drag so
it scrolls.

```
cargo run --example multiline_text_input
```