Stick REPL icon in quick action bar (#14064)

REPL Quick Actions

<img width="325" alt="image"
src="https://github.com/zed-industries/zed/assets/836375/faaf4c8f-ef12-4417-a9dd-158d5beae8ba">

When the Jupyter REPL is enabled and a kernel is available, show the
status in the editor bar:

![quick action bar
repl](https://github.com/zed-industries/zed/assets/836375/f3445283-f1fc-4714-895b-7aa842d4ab76)


Release Notes:

- N/A

---------

Co-authored-by: Nate Butler <iamnbutler@gmail.com>

crates/repl/src/kernels.rs

@@ -82,7 +82,7 @@ pub enum Kernel {
 }
 
 impl Kernel {
-    pub fn dot(&mut self) -> Indicator {
+    pub fn dot(&self) -> Indicator {
         match self {
             Kernel::RunningKernel(kernel) => match kernel.execution_state {
                 ExecutionState::Idle => Indicator::dot().color(Color::Success),