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/dap/src/client.rs

@@ -2,7 +2,7 @@ use crate::{
     adapters::DebugAdapterBinary,
     transport::{IoKind, LogKind, TransportDelegate},
 };
-use anyhow::{Result, anyhow};
+use anyhow::Result;
 use dap_types::{
     messages::{Message, Response},
     requests::Request,
@@ -187,10 +187,7 @@ impl DebugAdapterClient {
                     Ok(serde_json::from_value(Default::default())?)
                 }
             }
-            false => Err(anyhow!(
-                "Request failed: {}",
-                response.message.unwrap_or_default()
-            )),
+            false => anyhow::bail!("Request failed: {}", response.message.unwrap_or_default()),
         }
     }