Improve keymap json schema (#23044)

Also:

* Adds `impl_internal_actions!` for deriving the `Action` trait without
registering.

* Removes some deserializers that immediately fail in favor of
`#[serde(skip)]` on fields where they were used. This also omits them
from the schema.

Release Notes:

- Keymap settings file now has more JSON schema information to inform
`json-language-server` completions and info, particularly for actions
that take input.

crates/vim/src/digraph.rs

@@ -3,6 +3,7 @@ use std::sync::Arc;
 use collections::HashMap;
 use editor::Editor;
 use gpui::{impl_actions, AppContext, Keystroke, KeystrokeEvent};
+use schemars::JsonSchema;
 use serde::Deserialize;
 use settings::Settings;
 use std::sync::LazyLock;
@@ -12,7 +13,7 @@ use crate::{state::Operator, Vim, VimSettings};
 
 mod default;
 
-#[derive(PartialEq, Clone, Deserialize)]
+#[derive(Debug, Clone, Deserialize, JsonSchema, PartialEq)]
 struct Literal(String, char);
 impl_actions!(vim, [Literal]);