fix: prevent indentation shift for tree items without parent icons

[maruthang]

Fixes #307350

Summary

• When a collapsible parent item lacks an icon, alignIconWithTwisty() incorrectly triggered alignment for leaf children, hiding their twistie space (width: 0) while collapsible siblings kept theirs. This caused inconsistent indentation at the same depth level.
• Changed the "parent lacks icon" case in alignIconWithTwisty() to return false, so alignment only applies when the parent has an icon and can establish a consistent visual hierarchy.
• The "parent has icon" case (line 1653) remains unchanged and continues to work correctly.

Test plan

• Create a TreeView extension with mixed items:
  • Group items (collapsible) WITHOUT icons
  • Leaf items WITH icons
  • At the same depth level
• Verify that all items at the same depth have consistent indentation
• Verify group items WITH icons still produce correct alignment for their leaf children
• Verify toggling between grouped/ungrouped doesn't cause indentation shifts

[vs-code-engineering]

📬 CODENOTIFY

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

@bpasero

Matched files:

• src/vs/workbench/browser/parts/views/treeView.ts