fix(reorder-group): wait for content to render before getting scroll position

[willmartian]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: resolves #23875

What is the new behavior?

• Dragging a reorderable element now properly scrolls ion-content

Does this introduce a breaking change?

• Yes
• No

Other information

[liamdebeasi]

Can you make a dev build so I can test this in an app using custom elements build?

[willmartian]

Can you make a dev build so I can test this in an app using custom elements build?

@liamdebeasi, created dev build 6.0.0-dev.202110041416.8e2ffd7

I also tested this in the original repository submitted by the issue creator and it resolved the issue: https://github.com/tetsuwanadam/ionic_reorder_scroll