bug: issues on VitaminTextField for UIKit

[florentlotthepro]

Describe the bug

After the review of the VitaminTextField on UIKit, we identified some points to fix:

• [ ] The helper text is too close to the bottom of the text field. It should be at 2px (like the counter).
• [ ] The placeholder in dark mode is too visible (content tertiary).
• [ ] When the text field is filled, the text inside should be black (content primary).
• [ ] The label on the filled style should be grey (content tertiary).
• [ ] The text field's border in the active, error, and success states should have a thick of 2px.
• [ ] The text field's border in the disable state is more visible than when no disable > there must be a mistake.
• [ ] The icon for the filled style seems to be too high. It should at 4px of the text field.

Steps to reproduce

You can see it in the showcase.