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/project/src/debugger/locators/cargo.rs

@@ -1,4 +1,4 @@
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result};
 use async_trait::async_trait;
 use dap::{DapLocator, DebugRequest, adapters::DebugAdapterName};
 use gpui::SharedString;
@@ -90,11 +90,10 @@ impl DapLocator for CargoLocator {
     }
 
     async fn run(&self, build_config: SpawnInTerminal) -> Result<DebugRequest> {
-        let Some(cwd) = build_config.cwd.clone() else {
-            return Err(anyhow!(
-                "Couldn't get cwd from debug config which is needed for locators"
-            ));
-        };
+        let cwd = build_config
+            .cwd
+            .clone()
+            .context("Couldn't get cwd from debug config which is needed for locators")?;
         let builder = ShellBuilder::new(true, &build_config.shell).non_interactive();
         let (program, args) = builder.build(
             "cargo".into(),
@@ -119,9 +118,7 @@ impl DapLocator for CargoLocator {
         }
 
         let status = child.status().await?;
-        if !status.success() {
-            return Err(anyhow::anyhow!("Cargo command failed"));
-        }
+        anyhow::ensure!(status.success(), "Cargo command failed");
 
         let executables = output
             .lines()
@@ -133,9 +130,10 @@ impl DapLocator for CargoLocator {
                     .map(String::from)
             })
             .collect::<Vec<_>>();
-        if executables.is_empty() {
-            return Err(anyhow!("Couldn't get executable in cargo locator"));
-        };
+        anyhow::ensure!(
+            !executables.is_empty(),
+            "Couldn't get executable in cargo locator"
+        );
         let is_test = build_config.args.first().map_or(false, |arg| arg == "test");
 
         let mut test_name = None;
@@ -161,7 +159,7 @@ impl DapLocator for CargoLocator {
         };
 
         let Some(executable) = executable.or_else(|| executables.first().cloned()) else {
-            return Err(anyhow!("Couldn't get executable in cargo locator"));
+            anyhow::bail!("Couldn't get executable in cargo locator");
         };
 
         let args = test_name.into_iter().collect();