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/project/src/image_store.rs

@@ -2,7 +2,7 @@ use crate::{
     Project, ProjectEntryId, ProjectItem, ProjectPath,
     worktree_store::{WorktreeStore, WorktreeStoreEvent},
 };
-use anyhow::{Context as _, Result, anyhow};
+use anyhow::{Context as _, Result};
 use collections::{HashMap, HashSet, hash_map};
 use futures::{StreamExt, channel::oneshot};
 use gpui::{
@@ -128,7 +128,7 @@ impl ImageItem {
         let file_metadata = fs
             .metadata(image_path.as_path())
             .await?
-            .ok_or_else(|| anyhow!("failed to load image metadata"))?;
+            .context("failed to load image metadata")?;
 
         Ok(ImageMetadata {
             width,
@@ -223,7 +223,7 @@ impl ProjectItem for ImageItem {
         project: &Entity<Project>,
         path: &ProjectPath,
         cx: &mut App,
-    ) -> Option<Task<gpui::Result<Entity<Self>>>> {
+    ) -> Option<Task<anyhow::Result<Entity<Self>>>> {
         if is_image_file(&project, &path, cx) {
             Some(cx.spawn({
                 let path = path.clone();
@@ -702,7 +702,7 @@ fn create_gpui_image(content: Vec<u8>) -> anyhow::Result<Arc<gpui::Image>> {
             image::ImageFormat::Gif => gpui::ImageFormat::Gif,
             image::ImageFormat::Bmp => gpui::ImageFormat::Bmp,
             image::ImageFormat::Tiff => gpui::ImageFormat::Tiff,
-            _ => Err(anyhow::anyhow!("Image format not supported"))?,
+            format => anyhow::bail!("Image format {format:?} not supported"),
         },
         content,
     )))