docs(docs-infra): show usageNotes only for methods.

[JeanMeche]

Prior to this change, function and methods showed their usage notes which resulted in duplicate displays for functions.

Fixes #57339

Demo:

Without usages : https://ng-dev-previews-fw--pr-angular-angular-57343-adev-prev-l9nxcic9.web.app/api/core/output With usages : https://ng-dev-previews-fw--pr-angular-angular-57343-adev-prev-l9nxcic9.web.app/api/router/Router#navigateByUrl

[github-actions[bot]]

Deployed adev-preview for 0e69d2e48036df28d91b0506d3ff7be54a7240d9 to: https://ng-dev-previews-fw--pr-angular-angular-57343-adev-prev-l9nxcic9.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

[AndrewKushnir]

This PR was merged into the repository by commit e404f88092b1bdcd8fe6d3b09db95be85b81cfda.

The changes were merged into the following branches: main, 18.2.x

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