## Why / What

Fixes #58702.

In Helix mode the block cursor is a one-character selection that can
rest on the
trailing newline at the end of a line. When you select to the end of a
line
(excluding the newline) and press `d`, Helix leaves the cursor on the
newline.
Zed instead clamped the cursor onto the character immediately to the
left of the
deleted selection.

The shared `visual_delete` always re-clipped the post-deletion cursor at
line
ends (`set_clip_at_line_ends(true)`), which is correct for Vim normal
mode but
contradicts Helix mode, where `Vim::clip_at_line_ends()` is `false`.
This also
made Helix inconsistent with itself: deleting a whole line left the
cursor on the
newline, but deleting to the end of a non-empty line clamped it onto the
previous
character. The fix honors the active mode's clip policy, so Helix keeps
the
cursor on the newline.

## Testing

- Added `test_delete_to_end_of_line_keeps_cursor_on_newline` reproducing
#58702.
- Corrected `test_helix_select_end_of_line`; its mid-line assertion had
captured
the pre-fix (clamped) cursor position. Its whole-line assertion already
expected the cursor on the newline, so the test is now internally
consistent.
- `cargo test -p vim`: 540 passed, 0 failed.
- Vim visual-mode delete is unchanged (`is_helix()` is false for Vim
modes).

Release Notes:

- Fixed Helix mode placing the cursor on the wrong character after
deleting a selection that ends at the end of a line.

---------

Co-authored-by: dino <dinojoaocosta@gmail.com>