Closes #51693

Helix was unable to paste from the system clipboard, ex: `vim: paste`
would work but `helix: paste` would not work. Helix paste was silently
requiring the content it was going to paste to have selection metadata
exist, and just silently fail if it didn't, and the system clipboard
doesn't have that metadata. note: this is not necessarily for parity
with helix, as helix didn't seem to support this either in my testing,
but rather parity with the other parts of zed, editor mode and vim mode.

single-line paste:


https://github.com/user-attachments/assets/c8696032-d265-4025-9c4c-a8c35dfd2529

multi-line paste:


https://github.com/user-attachments/assets/4bf96033-e13d-4ec1-8a7e-8c56bbc12b94

I also added a new test verifying the behavior.

Before you mark this PR as ready for review, make sure that you have:
- [x] Added a solid test coverage and/or screenshots from doing manual
testing
- [x] Done a self-review taking into account security and performance
aspects
- [x] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

Release Notes:

- helix: fixed helix paste not pasting from system clipboard.