settings: accept trailing commas (#2606)

Z-2357

I've found a crate that handles both comments and trailing commas in
JSON. It is a fork of `serde_json`, but it is maintained & up-to-date.
Sadly RawValue seems to not play nicely with it; I've ran into
deserialisation issues around use of RawValue. For this PR I've migrated
to `Value` API.

Obviously this is just a point of discussion, not something I'd merge
straight away. There may be better solutions to this particular problem.

I've also noticed that `serde_json_lenient` does not handle trailing
commas after bindings array. I'm not sure how big of an issue that is.

Release Notes:
- Improved handling of trailing commas in settings files.
[#1322](https://github.com/zed-industries/community/issues/1322)

crates/gpui/src/app.rs

@@ -445,7 +445,7 @@ type WindowBoundsCallback = Box<dyn FnMut(WindowBounds, Uuid, &mut WindowContext
 type KeystrokeCallback =
     Box<dyn FnMut(&Keystroke, &MatchResult, Option<&Box<dyn Action>>, &mut WindowContext) -> bool>;
 type ActiveLabeledTasksCallback = Box<dyn FnMut(&mut AppContext) -> bool>;
-type DeserializeActionCallback = fn(json: &str) -> anyhow::Result<Box<dyn Action>>;
+type DeserializeActionCallback = fn(json: serde_json::Value) -> anyhow::Result<Box<dyn Action>>;
 type WindowShouldCloseSubscriptionCallback = Box<dyn FnMut(&mut AppContext) -> bool>;
 
 pub struct AppContext {
@@ -624,14 +624,14 @@ impl AppContext {
     pub fn deserialize_action(
         &self,
         name: &str,
-        argument: Option<&str>,
+        argument: Option<serde_json::Value>,
     ) -> Result<Box<dyn Action>> {
         let callback = self
             .action_deserializers
             .get(name)
             .ok_or_else(|| anyhow!("unknown action {}", name))?
             .1;
-        callback(argument.unwrap_or("{}"))
+        callback(argument.unwrap_or_else(|| serde_json::Value::Object(Default::default())))
             .with_context(|| format!("invalid data for action {}", name))
     }
 
@@ -5573,7 +5573,7 @@ mod tests {
         let action1 = cx
             .deserialize_action(
                 "test::something::ComplexAction",
-                Some(r#"{"arg": "a", "count": 5}"#),
+                Some(serde_json::from_str(r#"{"arg": "a", "count": 5}"#).unwrap()),
             )
             .unwrap();
         let action2 = cx