Use anyhow more idiomatically (#31052)

https://github.com/zed-industries/zed/issues/30972 brought up another
case where our context is not enough to track the actual source of the
issue: we get a general top-level error without inner error.

The reason for this was `.ok_or_else(|| anyhow!("failed to read HEAD
SHA"))?; ` on the top level.

The PR finally reworks the way we use anyhow to reduce such issues (or
at least make it simpler to bubble them up later in a fix).
On top of that, uses a few more anyhow methods for better readability.

* `.ok_or_else(|| anyhow!("..."))`, `map_err` and other similar error
conversion/option reporting cases are replaced with `context` and
`with_context` calls
* in addition to that, various `anyhow!("failed to do ...")` are
stripped with `.context("Doing ...")` messages instead to remove the
parasitic `failed to` text
* `anyhow::ensure!` is used instead of `if ... { return Err(...); }`
calls
* `anyhow::bail!` is used instead of `return Err(anyhow!(...));`

Release Notes:

- N/A

crates/repl/src/kernels/native_kernel.rs

@@ -351,14 +351,7 @@ impl RunningKernel for NativeRunningKernel {
     fn force_shutdown(&mut self, _window: &mut Window, _cx: &mut App) -> Task<anyhow::Result<()>> {
         self._process_status_task.take();
         self.request_tx.close_channel();
-
-        Task::ready(match self.process.kill() {
-            Ok(_) => Ok(()),
-            Err(error) => Err(anyhow::anyhow!(
-                "Failed to kill the kernel process: {}",
-                error
-            )),
-        })
+        Task::ready(self.process.kill().context("killing the kernel process"))
     }
 }