Right align actions tree view

[sam-shubham]

Fixes #251722

TreeView: Keep actions aligned during horizontal scrolling

On top of the initial offset computation introduced by @alexr00, this PR completes and stabilizes the right-aligned action behavior for TreeViews with horizontal scrolling.

Changes

• Keep actions aligned to the viewport’s right edge during horizontal scroll.
• Prevent applying the offset to nodes that do not contain action items
  (.monaco-list-row:has(.actions .action-item)).
• Ensure correct alignment without requiring an initial scroll.
• Preserve hover / selected / focused background consistency.
• Reset --list-scroll-right-offset when horizontal scrolling is disabled.
• Register --list-scroll-right-offset in vscode-known-variables.json.

Result

• Action buttons remain visually fixed while content scrolls.
• Nodes without actions are unaffected.
• No initial scroll required for correct alignment.
• Fully theme-aware and scoped to horizontal-scrolling TreeViews only.

Preview

Screen.Recording.2026-02-14.at.3.56.39.AM.mov

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@joaomoreno

Matched files:

• src/vs/base/browser/ui/list/listView.ts

@benibenj

Matched files:

• src/vs/base/browser/ui/list/listView.ts

@bpasero

Matched files:

• src/vs/workbench/browser/parts/views/media/views.css