Prevent the DOM updater from prematurely reusing the composition node

FIX: Fix an issue where changing decorations right before a composition could
end up corrupting the visible DOM.

Author: marijnh

src/buildtile.ts

@@ -457,7 +457,7 @@ export class TileUpdate {
           }
         } else if (tile.isText()) {
           this.builder.ensureLine(null)
-          if (!from && to == tile.length) {
+          if (!from && to == tile.length && !this.cache.reused.has(tile)) {
             this.builder.addText(tile.text, activeMarks, openMarks, this.cache.reuse(tile))
           } else {
             this.cache.add(tile)

src/docview.ts

@@ -122,6 +122,8 @@ export class DocView {
       if (composition || changes.length) {
         let oldTile = this.tile
         let builder = new TileUpdate(this.view, oldTile, this.blockWrappers, this.decorations, this.dynamicDecorationMap)
+        if (composition && Tile.get(composition.text))
+          builder.cache.reused.set(Tile.get(composition.text)!, Reused.DOM)
         this.tile = builder.run(changes, composition)
         destroyDropped(oldTile, builder.cache.reused)
       }