vim: Add sneak motion

[mrkajetanp]

Implement support for the vim sneak motion from the vim-sneak plugin. The motion jumps forward or backward to any location specified by two characters.

The Sneak & SneakBackward operators are bound to 'z' and 'Z' by default to avoid overwriting the 's' and 'S' default keybindings, similar to the way the original plugin uses 'z' with operators to avoid conflicts.

Reference:
https://github.com/justinmk/vim-sneak

Release Notes:

• Added support for the vim-sneak motion (#13858).

[cla-bot]

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[mrkajetanp]

@cla-bot check

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[mrnugget]

Wowow, this is already looking amazing! Before I dive too deep into the code, some thoughts/comments:

1. Can you add a test here? https://github.com/zed-industries/zed/blob/99385e5d12d7d35da386d3d2f19d010f25648596/crates/vim/src/test.rs
2. It doesn't look like this will work with multi-byte characters, right? Here's a test that ensures t works with them, you can maybe take a look at that one:

   zed/crates/vim/src/test.rs

   Lines 1298 to 1309 in 99385e5

   	#[gpui::test]
   	async fn test_find_multibyte(cx: &mut gpui::TestAppContext) {
   	let mut cx = NeovimBackedTestContext::new(cx).await;
   	cx.set_shared_state(r#"<label for="guests">ˇPočet hostů</label>"#)
   	.await;
   	cx.simulate_shared_keystrokes("c t < o escape").await;
   	cx.shared_state()
   	.await
   	.assert_eq(r#"<label for="guests">ˇo</label>"#);
   	}

3. This breaks zz keybinding, I assume. I don't think we should do that. How about we use a setting to disable this behavior? That way we could also use s. See here which other Vim settings there are already in use:

   zed/crates/vim/src/vim.rs

   Lines 1113 to 1120 in 99385e5

   	#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
   	struct VimSettingsContent {
   	pub use_system_clipboard: Option<UseSystemClipboard>,
   	pub use_multiline_find: Option<bool>,
   	pub use_smartcase_find: Option<bool>,
   	pub custom_digraphs: Option<HashMap<String, Arc<str>>>,
   	}

[ConradIrwin]

Thanks for this! Closing this for now due to a lack of activity, but this is a very highly requested feature. if you want to pair with me on getting this over the line: https://calendly.com/conradirwin/pairing