Runtimes UI Starter (#13625)

Initial runtimes UI panel. The main draw here is that all message
subscription occurs with two background tasks that run for the life of
the kernel. Follow on to #12062

* [x] Disable previous cmd-enter behavior only if runtimes are enabled
in settings
* [x] Only show the runtimes panel if it is enabled via settings
* [x] Create clean UI for the current sessions

### Running Kernels UI

<img width="205" alt="image"
src="https://github.com/zed-industries/zed/assets/836375/814ae79b-0807-4e23-bc95-77ce64f9d732">

* [x] List running kernels
* [x] Implement shutdown
* [x] Delete connection file on `drop` of `RunningKernel`
* [x] Implement interrupt

#### Project-specific Kernel Settings

- [x] Modify JupyterSettings to include a `kernel_selections` field
(`HashMap<String, String>`).
- [x] Implement saving and loading of kernel selections to/from
`.zed/settings.json` (by default, rather than global settings?)

#### Kernel Selection Persistence

- [x] Save the selected kernel for each language when the user makes a
choice.
- [x] Load these selections when the RuntimePanel is initialized.

#### Use Selected Kernels

- [x] Modify kernel launch to use the selected kernel for the detected
language.
- [x] Fallback to default behavior if no selection is made.

### Empty states

- [x] Create helpful UI for when the user has 0 kernels they can launch
and/or 0 kernels running

<img width="694" alt="image"
src="https://github.com/zed-industries/zed/assets/836375/d6a75939-e4e4-40fb-80fe-014da041cc3c">

## Future work

### Kernel Discovery

- Improve the kernel discovery process to handle various installation
methods (system, virtualenv, poetry, etc.).
- Create a way to refresh the available kernels on demand

### Documentation:

- Update documentation to explain how users can configure kernels for
their projects.
- Provide examples of .zed/settings.json configurations for kernel
selection.

### Kernel Selection UI

- Implement a new section in the RuntimePanel to display available
kernels.
- Group on the language name from the kernel specification 
- Create a dropdown for each language group to select the default
kernel.


Release Notes:

- N/A

---------

Co-authored-by: Kirill <kirill@zed.dev>

crates/zed/src/zed.rs

@@ -197,6 +197,10 @@ pub fn initialize_workspace(app_state: Arc<AppState>, cx: &mut AppContext) {
         cx.spawn(|workspace_handle, mut cx| async move {
             let assistant_panel =
                 assistant::AssistantPanel::load(workspace_handle.clone(), cx.clone());
+
+            // todo!(): enable/disable this based on settings
+            let runtime_panel = repl::RuntimePanel::load(workspace_handle.clone(), cx.clone());
+
             let project_panel = ProjectPanel::load(workspace_handle.clone(), cx.clone());
             let outline_panel = OutlinePanel::load(workspace_handle.clone(), cx.clone());
             let terminal_panel = TerminalPanel::load(workspace_handle.clone(), cx.clone());
@@ -214,6 +218,7 @@ pub fn initialize_workspace(app_state: Arc<AppState>, cx: &mut AppContext) {
                 outline_panel,
                 terminal_panel,
                 assistant_panel,
+                runtime_panel,
                 channels_panel,
                 chat_panel,
                 notification_panel,
@@ -222,6 +227,7 @@ pub fn initialize_workspace(app_state: Arc<AppState>, cx: &mut AppContext) {
                 outline_panel,
                 terminal_panel,
                 assistant_panel,
+                runtime_panel,
                 channels_panel,
                 chat_panel,
                 notification_panel,
@@ -229,6 +235,7 @@ pub fn initialize_workspace(app_state: Arc<AppState>, cx: &mut AppContext) {
 
             workspace_handle.update(&mut cx, |workspace, cx| {
                 workspace.add_panel(assistant_panel, cx);
+                workspace.add_panel(runtime_panel, cx);
                 workspace.add_panel(project_panel, cx);
                 workspace.add_panel(outline_panel, cx);
                 workspace.add_panel(terminal_panel, cx);
@@ -3188,6 +3195,7 @@ mod tests {
             outline_panel::init((), cx);
             terminal_view::init(cx);
             assistant::init(app_state.fs.clone(), app_state.client.clone(), cx);
+            repl::init(cx);
             tasks_ui::init(cx);
             initialize_workspace(app_state.clone(), cx);
             app_state