Fixes #131350

This PR is to remove the extra padding in `DropdownMenuEntry` if both the text field and the dropdown menu entry have leading icons.

**After** fix:
<img width="300" alt="Screenshot 2023-09-19 at 4 35 24 PM" src="https://github.com/flutter/flutter/assets/36861262/ed7d92a5-3f96-4106-a03e-09258ea3709f">

**Before** fix:
<img width="300" alt="Screenshot 2023-09-19 at 4 37 58 PM" src="https://github.com/flutter/flutter/assets/36861262/fdbfef54-6c93-48fb-bd64-41fa31dde531">