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/workspace/src/notifications.rs

@@ -1,4 +1,5 @@
 use crate::{SuppressNotification, Toast, Workspace};
+use anyhow::Context as _;
 use gpui::{
     AnyView, App, AppContext as _, AsyncWindowContext, ClickEvent, ClipboardItem, Context,
     DismissEvent, Entity, EventEmitter, FocusHandle, Focusable, PromptLevel, Render, ScrollHandle,
@@ -239,9 +240,9 @@ impl LanguageServerPrompt {
             });
 
             potential_future? // App Closed
-                .ok_or_else(|| anyhow::anyhow!("Response already sent"))?
+                .context("Response already sent")?
                 .await
-                .ok_or_else(|| anyhow::anyhow!("Stream already closed"))?;
+                .context("Stream already closed")?;
 
             this.update(cx, |_, cx| cx.emit(DismissEvent))?;