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/gpui/tests/action_macros.rs

@@ -1,12 +1,13 @@
 use gpui::{actions, impl_actions};
 use gpui_macros::register_action;
+use schemars::JsonSchema;
 use serde_derive::Deserialize;
 
 #[test]
 fn test_action_macros() {
     actions!(test, [TestAction]);
 
-    #[derive(PartialEq, Clone, Deserialize)]
+    #[derive(PartialEq, Clone, Deserialize, JsonSchema)]
     struct AnotherTestAction;
 
     impl_actions!(test, [AnotherTestAction]);