Add new field dropdown gets cutoff on tall forms

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- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-adminui/issues?q=is%3Aissue+).
- [X] I have read the guide for [submitting bug reports](https://github.com/aws-amplify/amplify-adminui/blob/main/CONTRIBUTING.md#bug-reports).
- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.
- [X] I have removed any sensitive information from my code snippets and submission.

### App Id

na

### Region

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### Environment name

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### Figma File Version (if applicable)

na

### Amplify CLI Version

na

### If applicable, what version of Node.js are you using?

na

### What operating system are you using?

na

### Browser type?

Chrome

### Describe the bug

The add new field dropdown in form builder gets cut off on long forms and when you try to add a new field at the bottom of the form.


### Expected behavior

The dropdown repositions and maybe opens upwards, or starts higher up to allow for more room to scroll.

### Reproduction steps

Create a long form that takes up most of the height of the UI. You can do this by continuing to add form fields in form builder's UI.

Try to add a new field at the bottom of the form, and the dropdown will not reposition so there is a little space to scroll through the dropdown.

### Project Identifier

_No response_

### Additional information

_No response_

Start in the form builder UI and reproduce the issue by creating a long form, then adding a field at the bottom in Chrome. The work is done when the add-new-field dropdown remains fully accessible, with enough space to scroll or repositioning upward instead of being cut off.

Written by the indexing model from the issue text.