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/gpui/src/window.rs

@@ -3922,7 +3922,7 @@ impl<V: 'static + Render> WindowHandle<V> {
                     .and_then(|window| window.root.clone())
                     .map(|root_view| root_view.downcast::<V>())
             })
-            .ok_or_else(|| anyhow!("window not found"))?
+            .context("window not found")?
             .map_err(|_| anyhow!("the type of the window's root view has changed"))?;
 
         Ok(x.read(cx))
@@ -4103,7 +4103,7 @@ impl TryInto<SharedString> for ElementId {
         if let ElementId::Name(name) = self {
             Ok(name)
         } else {
-            Err(anyhow!("element id is not string"))
+            anyhow::bail!("element id is not string")
         }
     }
 }