helix: Initial support for helix-mode paste (#37963)

This is a redo of #29776. I went for a separate function -- instead of
adding a bunch of conditions to `vim::Paste` -- because there were quite
a few differences.

Release Notes:

- Added a `vim::HelixPaste` command that imitates Helix's paste behavior

---------

Co-authored-by: Jakub Konka <kubkon@jakubkonka.com>

assets/keymaps/vim.json

@@ -433,6 +433,8 @@
       "h": "vim::WrappingLeft",
       "l": "vim::WrappingRight",
       "y": "vim::HelixYank",
+      "p": "vim::HelixPaste",
+      "shift-p": ["vim::HelixPaste", { "before": true }],
       "alt-;": "vim::OtherEnd",
       "ctrl-r": "vim::Redo",
       "f": ["vim::PushFindForward", { "before": false, "multiline": true }],