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/web_search_providers/src/cloud.rs

@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use anyhow::{Context as _, Result, anyhow};
+use anyhow::{Context as _, Result};
 use client::Client;
 use futures::AsyncReadExt as _;
 use gpui::{App, AppContext, Context, Entity, Subscription, Task};
@@ -96,9 +96,9 @@ async fn perform_web_search(
     } else {
         let mut body = String::new();
         response.body_mut().read_to_string(&mut body).await?;
-        return Err(anyhow!(
+        anyhow::bail!(
             "error performing web search.\nStatus: {:?}\nBody: {body}",
             response.status(),
-        ));
+        );
     }
 }