Implement RunningKernel trait for native and remote kernels (#20934)

This PR introduces a unified interface for both native and remote
kernels through the `RunningKernel` trait. When either the native kernel
or the remote kernels are started, they return a `Box<dyn
RunningKernel>` to make it easier to work with the session. As a bonus
of this refactor, I've dropped some of the mpsc channels to instead opt
for passing messages directly to `session.route(message)`. There was a
lot of simplification of `Session` by moving responsibilities to
`NativeRunningKernel`.

No release notes yet until this is finalized.

* [x] Detect remote kernelspecs from configured remote servers
* [x] Launch kernel on demand

For now, this allows you to set env vars `JUPYTER_SERVER` and
`JUPYTER_TOKEN` to access a remote server. `JUPYTER_SERVER` should be a
base path like `http://localhost:8888` or
`https://notebooks.gesis.org/binder/jupyter/user/rubydata-binder-w6igpy4l/`

Release Notes:

- N/A

crates/repl/src/kernels/mod.rs

@@ -6,7 +6,7 @@ use futures::{
     future::Shared,
     stream,
 };
-use gpui::{AppContext, Model, Task};
+use gpui::{AppContext, Model, Task, WindowContext};
 use language::LanguageName;
 pub use native_kernel::*;
 
@@ -16,7 +16,7 @@ pub use remote_kernels::*;
 
 use anyhow::Result;
 use runtimelib::{ExecutionState, JupyterKernelspec, JupyterMessage, KernelInfoReply};
-use ui::SharedString;
+use ui::{Icon, IconName, SharedString};
 
 pub type JupyterMessageChannel = stream::SelectAll<Receiver<JupyterMessage>>;
 
@@ -59,6 +59,19 @@ impl KernelSpecification {
             Self::Remote(spec) => spec.kernelspec.language.clone(),
         })
     }
+
+    pub fn icon(&self, cx: &AppContext) -> Icon {
+        let lang_name = match self {
+            Self::Jupyter(spec) => spec.kernelspec.language.clone(),
+            Self::PythonEnv(spec) => spec.kernelspec.language.clone(),
+            Self::Remote(spec) => spec.kernelspec.language.clone(),
+        };
+
+        file_icons::FileIcons::get(cx)
+            .get_type_icon(&lang_name.to_lowercase())
+            .map(Icon::from_path)
+            .unwrap_or(Icon::new(IconName::ReplNeutral))
+    }
 }
 
 pub fn python_env_kernel_specifications(
@@ -134,7 +147,7 @@ pub trait RunningKernel: Send + Debug {
     fn set_execution_state(&mut self, state: ExecutionState);
     fn kernel_info(&self) -> Option<&KernelInfoReply>;
     fn set_kernel_info(&mut self, info: KernelInfoReply);
-    fn force_shutdown(&mut self) -> anyhow::Result<()>;
+    fn force_shutdown(&mut self, cx: &mut WindowContext) -> Task<anyhow::Result<()>>;
 }
 
 #[derive(Debug, Clone)]