Remove iterators from IDecorationService

They're too low performance for typical use cases

Fixes #4079

src/browser/renderer/dom/DomRendererRowFactory.ts

@@ -204,9 +204,9 @@ export class DomRendererRowFactory {
       let bgOverride: IColor | undefined;
       let fgOverride: IColor | undefined;
       let isTop = false;
-      for (const d of this._decorationService.getDecorationsAtCell(x, row)) {
+      this._decorationService.forEachDecorationAtCell(x, row, undefined, d => {
         if (d.options.layer !== 'top' && isTop) {
-          continue;
+          return;
         }
         if (d.backgroundColorRGB) {
           bgColorMode = Attributes.CM_RGB;
@@ -219,7 +219,7 @@ export class DomRendererRowFactory {
           fgOverride = d.foregroundColorRGB;
         }
         isTop = d.options.layer === 'top';
-      }
+      });
 
       // Apply selection foreground if applicable
       const isInSelection = this._isCellInSelection(x, row);