Bump serialize-javascript and @angular-devkit/build-angular in /basic

Removes [serialize-javascript](https://github.com/yahoo/serialize-javascript). It's no longer used after updating ancestor dependency [@angular-devkit/build-angular](https://github.com/angular/angular-cli). These dependencies need to be updated together.


Removes `serialize-javascript`

Updates `@angular-devkit/build-angular` from 19.2.20 to 21.2.12
- [Release notes](https://github.com/angular/angular-cli/releases)
- [Changelog](https://github.com/angular/angular-cli/blob/main/CHANGELOG.md)
- [Commits](angular/angular-cli@v19.2.20...v21.2.12)

---
updated-dependencies:
- dependency-name: serialize-javascript
  dependency-version:
  dependency-type: indirect
- dependency-name: "@angular-devkit/build-angular"
  dependency-version: 21.2.12
  dependency-type: direct:development
...

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Author: dependabot[bot]