docs(aio): fix typo in "preserveWhitespaces" example

[benbraou]

Fixes #22147

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• 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?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

The property name is "preserveWhiteSpaces" with uppercase "s" after "preserveWhite" (but should be "preserveWhitespaces" with lowercase "s" after "preserveWhite")

What is the new behavior?

preserveWhitespaces is used instead

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

Maybe this PR should be merged after #22027 ? To avoid merge conflicts in aot-compiler.md for that PR ?

[IgorMinar]

thanks!

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