[Platforms]: UIShell html structure bugs

[alisonjoseph]

Summary

There are a couple of issues within SideNav when using type="RAIL_PANEL".

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1. Incorrect rendered HTML

The current rendered HTML structure for the SideNav is not correct. Specifically, popovers and tooltips are not being rendered inside their <li> elements.

Expected HTML structure:

<ul>
  <li>...</li>
  <li>...</li>
  <li>...</li>
  ...
</ul>

---

2. Inline styles in SideNavFlyoutMenu.tsx

Inline styles are currently being used to control visibility in SideNavFlyoutMenu.tsx. These should be removed and replaced with class names and CSS.

Current code:

<div style={{ display: isButtonFocused ? 'none' : 'block' }}>
  {flyoutMenuItems}
</div>