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/livekit_client/src/livekit_client.rs

@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use anyhow::Result;
+use anyhow::{Context as _, Result};
 use collections::HashMap;
 use futures::{SinkExt, channel::mpsc};
 use gpui::{App, AsyncApp, ScreenCaptureSource, ScreenCaptureStream, Task};
@@ -160,7 +160,7 @@ impl LocalParticipant {
         })?
         .await?
         .map(LocalTrackPublication)
-        .map_err(|error| anyhow::anyhow!("failed to publish track: {error}"))
+        .context("publishing a track")
     }
 
     pub async fn unpublish_track(
@@ -172,7 +172,7 @@ impl LocalParticipant {
         Tokio::spawn(cx, async move { participant.unpublish_track(&sid).await })?
             .await?
             .map(LocalTrackPublication)
-            .map_err(|error| anyhow::anyhow!("failed to unpublish track: {error}"))
+            .context("unpublishing a track")
     }
 }