refactor(@angular/ssr): use appRef.whenStable instead of util functio…

[sheikalthaf]

…n from angular core

using application whenStable function instead of custom util function from angular core.

PR Checklist

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• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
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• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[alan-agius4]

LGTM, thanks for your contribution.

[clydin]

The changes were merged into the following branches: main, 19.0.x

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