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/languages/src/tailwind.rs

@@ -1,4 +1,4 @@
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result};
 use async_trait::async_trait;
 use collections::HashMap;
 use futures::StreamExt;
@@ -198,20 +198,17 @@ async fn get_cached_server_binary(
                 last_version_dir = Some(entry.path());
             }
         }
-        let last_version_dir = last_version_dir.ok_or_else(|| anyhow!("no cached binary"))?;
+        let last_version_dir = last_version_dir.context("no cached binary")?;
         let server_path = last_version_dir.join(SERVER_PATH);
-        if server_path.exists() {
-            Ok(LanguageServerBinary {
-                path: node.binary_path().await?,
-                env: None,
-                arguments: server_binary_arguments(&server_path),
-            })
-        } else {
-            Err(anyhow!(
-                "missing executable in directory {:?}",
-                last_version_dir
-            ))
-        }
+        anyhow::ensure!(
+            server_path.exists(),
+            "missing executable in directory {last_version_dir:?}"
+        );
+        Ok(LanguageServerBinary {
+            path: node.binary_path().await?,
+            env: None,
+            arguments: server_binary_arguments(&server_path),
+        })
     })
     .await
     .log_err()