feat(virtual-scroll): usage with custom scroll target

[sean-perkins]

Updates the sections for note regarding Ionic components to include the usage instructions for the custom scroll target.

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[liamdebeasi]

Good to merge once my comment below is addressed.

[lincolnthree]

Hi all. Please see the following pull request in the Angular CDK, as I believe this will make much of this easier if we can get these features merged: angular/components#24394

This PR adds the ability to provide custom virtual scroll extensions to link with scroll containers. Essentially allowing the virtual-scroller to attach to ion-content's 'main' scrolling element directly (though I am attempting to work with the author to get that feature added / supported.)

Would love your comments & feedback.

[sean-perkins]

@lincolnthree that feature change would allow developers to make use of the ion-content's scroll container instead of the virtual scroll container, but the implementation code may be more difficult for implementers to follow:

<ion-content #content>
  <cdk-virtual-scroll-viewport [scrollableElement]="content.getScrollElement() | async">
    ...
 </cdk-virtual-scroll-viewport>
</ion-content>

I don't see any downsides to that feature change, but we would continue to offer this class approach to support all virtual scrolling solutions in all supported frameworks, not just CDK & Angular.

For example, this is how it looks for React, Vue and Angular with the same implementation pattern: https://gist.github.com/sean-perkins/277524ef0e450591907a87acec15af11

Appreciate your feedback and making us aware of that feature/change from Angular!

[Albert-Gao]

with this being merged, i guess this doc is outdated? https://ionicframework.com/docs/react/virtual-scroll#a-note-on-ionic-components :)

[avalanche1]

@sean-perkins pls deprecate https://ionicframework.com/docs/react/virtual-scroll#a-note-on-ionic-components as obsolete

[liamdebeasi]

Thanks everyone, I fixed this in #2780.