fix(overlays): define children custom elements

[sean-perkins]

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?

The child custom element ion-picker-column is never defined by ion-picker.

Issue Number: #24366

What is the new behavior?

ion-picker will define ion-picker-column when the controller is constructed.

Updated our internal API for createController and createOverlay to support defining custom children elements.

Does this introduce a breaking change?

• Yes
• No

Other information

[liamdebeasi]

Small readability issue, but otherwise looks good

[averyjohnston]

Looks great 👍