Pass the old widget value to WidgetType.updateDOM

FEATURE: `WidgetType.updateDOM` is now called with the previous widget value
as third argument.

See https://discuss.codemirror.net/t/accessing-other-instance-in-widgettype-updatedom/9693

Author: marijnh

src/buildtile.ts

@@ -324,7 +324,7 @@ class TileCache {
       let tile = widgets[i]
       if (!this.reused.has(tile) &&
           (pass == 0 ? tile.widget.compare(widget)
-            : tile.widget.constructor == widget.constructor && widget.updateDOM(tile.dom, this.view))) {
+            : tile.widget.constructor == widget.constructor && widget.updateDOM(tile.dom, this.view, tile.widget))) {
         widgets.splice(i, 1)
         if (i < this.index[0]) this.index[0]--
         if (tile.widget == widget && tile.length == length && (tile.flags & (TileFlag.Widget | TileFlag.BreakAfter)) == flags) {

src/decoration.ts

@@ -121,7 +121,7 @@ export abstract class WidgetType {
   /// true to indicate that it could update, false to indicate it
   /// couldn't (in which case the widget will be redrawn). The default
   /// implementation just returns false.
-  updateDOM(dom: HTMLElement, view: EditorView): boolean { return false }
+  updateDOM(dom: HTMLElement, view: EditorView, from: WidgetType): boolean { return false }
 
   /// @internal
   compare(other: WidgetType): boolean {