Remove iterators from IDecorationService

They're too low performance for typical use cases

Fixes #4079

addons/xterm-addon-canvas/src/TextRenderLayer.ts

@@ -187,15 +187,15 @@ export class TextRenderLayer extends BaseRenderLayer {
       // Get any decoration foreground/background overrides, this must be fetched before the early
       // exist but applied after inverse
       let isTop = false;
-      for (const d of this._decorationService.getDecorationsAtCell(x, this._bufferService.buffer.ydisp + y)) {
+      this._decorationService.forEachDecorationAtCell(x, this._bufferService.buffer.ydisp + y, undefined, d => {
         if (d.options.layer !== 'top' && isTop) {
-          continue;
+          return;
         }
         if (d.backgroundColorRGB) {
           nextFillStyle = d.backgroundColorRGB.css;
         }
         isTop = d.options.layer === 'top';
-      }
+      });
 
       if (prevFillStyle === null) {
         // This is either the first iteration, or the default background was set. Either way, we