Add static Runnables (#8009)

Part of #7108

This PR includes just the static runnables part. We went with **not**
having a dedicated panel for runnables.
This is just a 1st PR out of N, as we want to start exploring the
dynamic runnables front. Still, all that work is going to happen once
this gets merged.

Release Notes:

- Added initial, static Runnables support to Zed. Such runnables are defined in
`runnables.json` file (accessible via `zed: open runnables` action) and
they can be spawned with `runnables: spawn` action.

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>
Co-authored-by: Pitor <pitor@zed.dev>
Co-authored-by: Beniamin <beniamin@zagan.be>

crates/zed/src/languages/json.rs

@@ -53,7 +53,7 @@ impl JsonLspAdapter {
             },
             cx,
         );
-
+        let runnables_schema = runnable::static_source::DefinitionProvider::generate_json_schema();
         serde_json::json!({
             "json": {
                 "format": {
@@ -70,6 +70,10 @@ impl JsonLspAdapter {
                     {
                         "fileMatch": [schema_file_match(&paths::KEYMAP)],
                         "schema": KeymapFile::generate_json_schema(&action_names),
+                    },
+                    {
+                        "fileMatch": [schema_file_match(&paths::RUNNABLES)],
+                        "schema": runnables_schema,
                     }
                 ]
             }