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/src/gpui.rs

@@ -102,7 +102,9 @@ mod window;
 /// Do not touch, here be dragons for use by gpui_macros and such.
 #[doc(hidden)]
 pub mod private {
+    pub use anyhow;
     pub use linkme;
+    pub use schemars;
     pub use serde;
     pub use serde_derive;
     pub use serde_json;