fix(@angular/build): add webcontainer support for Vitest browser provider

[clydin]

Currently, Vitest's browser providers (playwright, webdriverio) are not compatible with webcontainer environments. This change introduces detection for webcontainers and and automatically configures the Vitest unit test builder to use the @vitest/browser-preview provider when running within a webcontainer.

This ensures that browser-based unit tests can execute correctly in webcontainer environments, providing a more consistent development experience across different platforms. The user is notified when the webcontainer environment is detected and the preview provider is activated. Dependency checks are also updated to ensure the correct @vitest/browser-preview package is installed when needed.

NOTE: For advanced scenarios, a custom runner config can be used to customize the browser configuration instead of using the builtin --browsers option and its automatic configuration.

[clydin]

This PR was merged into the repository. The changes were merged into the following branches:

• main: 50072cd
• 21.0.x: 63c9874

[yjaaidi]

❤️
Thank you for this as it closes #31654

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