fix(@angular-devkit/build-angular): reduce fast sourcemap threshold

High fidelity sourcemap processing can be expensive for larger bundle sizes.  This reduces the threshold to the original 500KB value to improve performance.

(cherry picked from commit d2dce46)

packages/angular_devkit/build_angular/src/utils/process-bundle.ts

@@ -29,8 +29,8 @@ import { I18nOptions } from './i18n-options';
 const cacache = require('cacache');
 const deserialize = ((v8 as unknown) as { deserialize(buffer: Buffer): unknown }).deserialize;
 
-// If code size is larger than 1MB, consider lower fidelity but faster sourcemap merge
-const FAST_SOURCEMAP_THRESHOLD = 1024 * 1024;
+// If code size is larger than 500KB, consider lower fidelity but faster sourcemap merge
+const FAST_SOURCEMAP_THRESHOLD = 500 * 1024;
 
 export interface ProcessBundleOptions {
   filename: string;