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/workspace/Cargo.toml

@@ -16,7 +16,7 @@ test-support = [
     "project/test-support",
     "settings/test-support",
     "gpui/test-support",
-    "fs/test-support"
+    "fs/test-support",
 ]
 
 [dependencies]
@@ -40,6 +40,7 @@ node_runtime.workspace = true
 parking_lot.workspace = true
 postage.workspace = true
 project.workspace = true
+runnable.workspace = true
 schemars.workspace = true
 serde.workspace = true
 serde_derive.workspace = true