feat(ui): add isStriped prop to TreeView component (#36649)

[Kaasfonthijn]

Description

This PR adds an optional isStriped prop to the TreeView component that enables alternating background colors for tree items, improving readability when items span multiple lines or can be expanded/collapsed.

Problem

As described in the feature request, the actions list in UI mode can be difficult to scan because:

• Some actions (like timeouts) are only one line
• Other actions span two lines (e.g., getByText('Heute'))
• Without visual separation, it's hard to distinguish between adjacent items

Solution

• Added isStriped?: boolean prop to TreeViewProps
• Applied tree-view-striped CSS class conditionally when isStriped={true}
• Updated CSS to use --vscode-tree-tableOddRowsBackground for theme-aware alternating backgrounds
• Enabled striped background for the actions tree in trace viewer
• Keep it flexible so the Tests overview has the old styling

Points of interest

• I removed unused styling in the treeview.css (.tree-view-entry.info and tree-view-entry.warning)

Screenshots

Old:

New:

With errors and expanded tree items:

Fixes #36649

[Kaasfonthijn]

@microsoft-github-policy-service agree

[dgozman]

@Kaasfonthijn Thank you for the PR! Unfortunately, there has been some misunderstanding on the issue this PR is fixing. I have discussed it with the team and captured the discussion here.

I will close this PR, as we do not plan to introduce striped background. Thank you for sending the PR though!