Fix type and import errors introduced by previous changes

FIX: Fix accidental non-optional field in layer config objects.

src/docview.ts

@@ -9,7 +9,7 @@ import {getAttrs} from "./attributes"
 import {clientRectsFor, isEquivalentPosition, maxOffset, Rect, scrollRectIntoView,
         getSelection, hasSelection, textRange, DOMSelectionState} from "./dom"
 import {ViewUpdate, decorations as decorationsFacet, outerDecorations,
-        ChangedRange, ScrollTarget, getScrollMargins, requestMeasureOnDocUpdate} from "./extension"
+        ChangedRange, ScrollTarget, getScrollMargins} from "./extension"
 import {EditorView} from "./editorview"
 import {Direction} from "./bidi"
 

src/layer.ts

@@ -200,7 +200,7 @@ interface LayerConfig {
   update(update: ViewUpdate, layer: HTMLElement): boolean
   /// Whether to update this layer every time the document view
   /// changes. Defaults to true.
-  updateOnDocViewUpdate: boolean
+  updateOnDocViewUpdate?: boolean
   /// Build a set of markers for this layer, and measure their
   /// dimensions.
   markers(view: EditorView): readonly LayerMarker[]