fix(unity-bootstrap-theme): updated anchor menu logic to account for …

[davidornelas11]

…header height

Description

This update is mainly to match the webspark-ci repo PR but the logic in the anchor menu js file in webspark-ci should match the code in this unity repo

Links

• JIRA ticket

FOR APPROVERS

• Percy build approval

Checklist

• [x] Unity project successfully builds from root yarn install & yarn build
• [x] Commits do not contain multiple scopes
• [x] Add/updated examples
• [x] Add/updated READMEs/docs
• [x] No new console errors
• [x] Accessibility checks

Browsers

• [ ] Chrome
• [ ] Safari
• [ ] Firefox
• [ ] Edge

Images