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/util/src/paths.rs

@@ -34,7 +34,7 @@ pub trait PathExt {
         }
         #[cfg(windows)]
         {
-            use anyhow::anyhow;
+            use anyhow::Context as _;
             use tendril::fmt::{Format, WTF8};
             WTF8::validate(bytes)
                 .then(|| {
@@ -43,7 +43,7 @@ pub trait PathExt {
                         OsStr::from_encoded_bytes_unchecked(bytes)
                     }))
                 })
-                .ok_or_else(|| anyhow!("Invalid WTF-8 sequence: {bytes:?}"))
+                .with_context(|| format!("Invalid WTF-8 sequence: {bytes:?}"))
         }
     }
 }

crates/util/src/util.rs

@@ -27,7 +27,7 @@ use std::{
 use unicase::UniCase;
 
 #[cfg(unix)]
-use anyhow::{Context as _, anyhow};
+use anyhow::Context as _;
 
 pub use take_until::*;
 #[cfg(any(test, feature = "test-support"))]
@@ -335,9 +335,7 @@ pub fn load_login_shell_environment() -> Result<()> {
     )
     .output()
     .context("failed to spawn login shell to source login environment variables")?;
-    if !output.status.success() {
-        Err(anyhow!("login shell exited with error"))?;
-    }
+    anyhow::ensure!(output.status.success(), "login shell exited with error");
 
     let stdout = String::from_utf8_lossy(&output.stdout);