ng serve with @angular/build: DevTools file search not working

### Command

serve

### Is this a regression?

- [x] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

angular19 with @angular-devkit/build-angular

### Description

When I try to migrate an Angular 20 project from @angular-devkit/build-angular to the new @angular/build, I notice that when running `ng serve` and opening the browser DevTools → Sources, searching for content across all files does not return any results.

### Minimal Reproduction

Angular versions: 20, 21, and 22 (out of the box)
Browser: Edge and Chrome
Operating System: Windows and Linux
SSR: off
Zoneless: off

Steps:
1. Create a new Angular app with `ng new v20`.
2. Run `ng serve`.
3. Open the browser and go to DevTools → Sources.
4. Try to search for content across all files.

Steps:
1. Create a new Angular app with `ng new v22`.
2. Run `ng serve`.
3. Open the browser and go to DevTools → Sources.
4. Try to search for content across all files.

### Exception or Error

```text

```

### Your Environment

```text
Angular CLI: 20.3.31
Node: 22.14.0
Package Manager: npm 10.9.2
OS: linux x64

Angular: 20.3.25
... common, compiler, compiler-cli, core, forms
... platform-browser, router

Package Version
------------------------------------
@angular-devkit/architect 0.2003.31
@angular-devkit/core 20.3.31
@angular-devkit/schematics 20.3.31
@angular/build 20.3.31
@angular/cli 20.3.31
@schematics/angular 20.3.31
rxjs 7.8.2
typescript 5.9.3
zone.js 0.15.1

---------------------------------------

Angular CLI : 22.0.5
Angular : 22.0.5
Node.js : 24.18.0
Package Manager : npm 11.16.0
Operating System : linux x64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build │ 22.0.5 │ ^22.0.5 │
│ @angular/cli │ 22.0.5 │ ^22.0.5 │
│ @angular/common │ 22.0.5 │ ^22.0.0 │
│ @angular/compiler │ 22.0.5 │ ^22.0.0 │
│ @angular/compiler-cli │ 22.0.5 │ ^22.0.0 │
│ @angular/core │ 22.0.5 │ ^22.0.0 │
│ @angular/forms │ 22.0.5 │ ^22.0.0 │
│ @angular/platform-browser │ 22.0.5 │ ^22.0.0 │
│ @angular/router │ 22.0.5 │ ^22.0.0 │
│ rxjs │ 7.8.2 │ ~7.8.0 │
│ typescript │ 6.0.3 │ ~6.0.2 │
│ vitest │ 4.1.9 │ ^4.0.8 │
└───────────────────────────┴───────────────────┴───────────────────┘
```

### Anything else relevant?

Angula version: 19 (out of the box)
Browser: Edge and Chrome
Operating System: Windows and Linux
SSR: off

Steps:
1. Create a new Angular app with `ng new v19`.
2. Run `ng serve`.
3. Open the browser and go to DevTools → Sources.
4. Try to search for content across all files.

Result:
The search works correctly in Angular 19.

Angular CLI: 19.2.27
Node: 22.14.0
Package Manager: npm 10.9.2
OS: linux x64

Angular: 19.2.25
... common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package Version
---------------------------------------------------------
@angular-devkit/architect 0.1902.27
@angular-devkit/build-angular 19.2.27
@angular-devkit/core 19.2.27
@angular-devkit/schematics 19.2.27
@angular/cli 19.2.27
@schematics/angular 19.2.27
rxjs 7.8.2
typescript 5.7.3
zone.js 0.15.1

使用 `ng serve` 和 `@angular/build` 建立新的 Angular 應用程式來重現問題，然後與使用 `@angular-devkit/build-angular` 的 Angular 19 進行比較。檢查 serve 輸出如何在 Chrome 或 Edge DevTools Sources 中公開。完成的標準是：在 Angular 20+ 中，跨檔案搜尋能像在 Angular 19 中一樣傳回內容，且相關回歸已由專案的測試涵蓋。

由索引模型根據 Issue 內容生成。