…Bottom button with 16px or less scroll buffer (#24489)

## **Description**

- Removes 16px buffer
- Allow optional scroll buffer in useScrollRequired hook

## **Related issues**

Fixes: #24485

## **Manual testing steps**

1. Create sign request from OpenSea login
2. Observe scroll behavior 

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**


https://github.com/MetaMask/metamask-extension/assets/20778143/1b436528-b285-41c0-a365-98ce2aed7eec

### **After**


https://github.com/MetaMask/metamask-extension/assets/20778143/4a42022a-1473-4f9c-b3a5-459510f221c2

## **Pre-merge author checklist**

- [ ] I’ve followed [MetaMask Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/CODING_GUIDELINES.md).
- [ ] I've completed the PR template to the best of my ability
- [ ] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.