vim: Update anchor used for LSP operations

[dinocosta]

Objective

Followup to #55542 , ensuring that we apply the same anchor calculation logic when performing hover, go to definition, go to declaration, go to type definition, go to implementation, find all references, go to reference, hover and document highlights.

• Describe the objective or issue this PR addresses.
• If you're fixing a specific issue, use "Fixes #X" for each issue as described in the GitHub docs.

Solution

In helix and vim visual modes, the head of a forward selection is its exclusive end, so it sits one position past the rendered block cursor. Operations targeting the symbol under the cursor queried the head directly and could miss the symbol entirely, for example, landing in the whitespace after a w motion.

The changes in #55542 fixed this for the case when renaming a symbol, but there's other places where Selection::head was still being used.

hover, go to definition, go to declaration, go to type definition, go to implementation, find all references, go to reference, hover and document highlights.

Testing

Tested both manually as well as introduced a new test for the go to definition case – vim::helix::test::test_helix_go_to_definition_uses_visible_cursor_position .

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Showcase

Go To Definition • Before

CleanShot.2026-07-03.at.17.53.25.mp4

Go To Definition • After

CleanShot.2026-07-03.at.17.54.48.mp4

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Release Notes:

• Improved LSP symbol operations (go to definition, find all references, hover, etc.) missing the symbol under the visible selection in Helix mode.