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/settings/src/settings.rs

@@ -36,3 +36,7 @@ pub fn initial_user_settings_content() -> Cow<'static, str> {
 pub fn initial_local_settings_content() -> Cow<'static, str> {
     asset_str::<SettingsAssets>("settings/initial_local_settings.json")
 }
+
+pub fn initial_runnables_content() -> Cow<'static, str> {
+    asset_str::<SettingsAssets>("settings/initial_runnables.json")
+}