Prevent stack overflow via Array.splice when updating big content views

FIX: Avoid a stack overflow that could happen when updating a line with a
lot of text tokens.

Issue codemirror/dev#1445

src/contentview.ts

@@ -199,7 +199,8 @@ export abstract class ContentView {
       let child = this.children[i]
       if (child.parent == this && children.indexOf(child) < 0) child.destroy()
     }
-    this.children.splice(from, to - from, ...children)
+    if (children.length < 250) this.children.splice(from, to - from, ...children)
+    else this.children = ([] as ContentView[]).concat(this.children.slice(0, from), children, this.children.slice(to))
     for (let i = 0; i < children.length; i++) children[i].setParent(this)
   }