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/livekit_api/src/livekit_api.rs

@@ -1,7 +1,7 @@
 pub mod proto;
 pub mod token;
 
-use anyhow::{Result, anyhow};
+use anyhow::Result;
 use async_trait::async_trait;
 use prost::Message;
 use reqwest::header::CONTENT_TYPE;
@@ -79,12 +79,12 @@ impl LiveKitClient {
                 Ok(Res::decode(response.bytes().await?)?)
             } else {
                 log::error!("Response {}: {:?}", url, response.status());
-                Err(anyhow!(
+                anyhow::bail!(
                     "POST {} failed with status code {:?}, {:?}",
                     url,
                     response.status(),
                     response.text().await
-                ))
+                );
             }
         }
     }

crates/livekit_api/src/token.rs

@@ -1,4 +1,4 @@
-use anyhow::{Result, anyhow};
+use anyhow::Result;
 use jsonwebtoken::{DecodingKey, EncodingKey, Header, Validation};
 use serde::{Deserialize, Serialize};
 use std::{
@@ -74,9 +74,7 @@ pub fn create(
     video_grant: VideoGrant,
 ) -> Result<String> {
     if video_grant.room_join.is_some() && identity.is_none() {
-        Err(anyhow!(
-            "identity is required for room_join grant, but it is none"
-        ))?;
+        anyhow::bail!("identity is required for room_join grant, but it is none");
     }
 
     let now = SystemTime::now();