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/elements/img.rs

@@ -5,7 +5,7 @@ use crate::{
     SMOOTH_SVG_SCALE_FACTOR, SharedString, SharedUri, StyleRefinement, Styled, SvgSize, Task,
     Window, px, swap_rgba_pa_to_bgra,
 };
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result};
 
 use futures::{AsyncReadExt, Future};
 use image::{
@@ -595,7 +595,7 @@ impl Asset for ImageAssetLoader {
                     let mut response = client
                         .get(uri.as_ref(), ().into(), true)
                         .await
-                        .map_err(|e| anyhow!(e))?;
+                        .with_context(|| format!("loading image asset from {uri:?}"))?;
                     let mut body = Vec::new();
                     response.body_mut().read_to_end(&mut body).await?;
                     if !response.status().is_success() {