Closes #5133 and discussion
https://github.com/zed-industries/zed/discussions/33493

This PR adds two new commands to select next/previous siblings in the
syntax tree. These commands were modelled after the existing ones about
expand/shrink selection. With this PR I've added new key bindings
inspired by `helix` for previous / next / expand / shrink selections.



https://github.com/user-attachments/assets/4ef7fadb-0b82-4897-95c7-1737827bf4ac


Release Notes:

- Add commands to select next/previous siblings in the syntax tree

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Co-authored-by: Joseph T. Lyons <JosephTLyons@gmail.com>