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/editor/src/editor.rs

@@ -5552,7 +5552,7 @@ impl Editor {
                 task.await?;
             }
 
-            Ok::<_, anyhow::Error>(())
+            anyhow::Ok(())
         })
         .detach_and_log_err(cx);
     }
@@ -10630,8 +10630,8 @@ impl Editor {
                 .map(|line| {
                     line.strip_prefix(&line_prefix)
                         .or_else(|| line.trim_start().strip_prefix(&line_prefix.trim_start()))
-                        .ok_or_else(|| {
-                            anyhow!("line did not start with prefix {line_prefix:?}: {line:?}")
+                        .with_context(|| {
+                            format!("line did not start with prefix {line_prefix:?}: {line:?}")
                         })
                 })
                 .collect::<Result<Vec<_>, _>>()
@@ -17330,7 +17330,7 @@ impl Editor {
             Err(err) => {
                 let message = format!("Failed to copy permalink: {err}");
 
-                Err::<(), anyhow::Error>(err).log_err();
+                anyhow::Result::<()>::Err(err).log_err();
 
                 if let Some(workspace) = workspace {
                     workspace
@@ -17385,7 +17385,7 @@ impl Editor {
             Err(err) => {
                 let message = format!("Failed to open permalink: {err}");
 
-                Err::<(), anyhow::Error>(err).log_err();
+                anyhow::Result::<()>::Err(err).log_err();
 
                 if let Some(workspace) = workspace {
                     workspace