Fixes #136162

This PR is to fix the floating `SnackBar` issue so that when the top of the bottom bar is higher than the top of the FAB, the snack bar will still float and not be clipped.

| Before fix | After fix |
|--------|--------|
| ![Screenshot 2023-10-11 at 1 54 30 PM](https://github.com/flutter/flutter/assets/36861262/dbe02312-1a80-4532-9bad-a8f162a6a942) | ![Screenshot 2023-10-11 at 1 54 52 PM](https://github.com/flutter/flutter/assets/36861262/68211de0-f04f-4b1a-b554-baf6a8e2f947)
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