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/language/src/language_registry.rs

@@ -873,15 +873,13 @@ impl LanguageRegistry {
                                 }
                             }
                             Err(e) => {
-                                log::error!("failed to load language {name}:\n{:?}", e);
+                                log::error!("failed to load language {name}:\n{e:?}");
                                 let mut state = this.state.write();
                                 state.mark_language_loaded(id);
                                 if let Some(mut txs) = state.loading_languages.remove(&id) {
                                     for tx in txs.drain(..) {
                                         let _ = tx.send(Err(anyhow!(
-                                            "failed to load language {}: {}",
-                                            name,
-                                            e
+                                            "failed to load language {name}: {e}",
                                         )));
                                     }
                                 }
@@ -944,7 +942,7 @@ impl LanguageRegistry {
                                 let grammar_name = wasm_path
                                     .file_stem()
                                     .and_then(OsStr::to_str)
-                                    .ok_or_else(|| anyhow!("invalid grammar filename"))?;
+                                    .context("invalid grammar filename")?;
                                 anyhow::Ok(with_parser(|parser| {
                                     let mut store = parser.take_wasm_store().unwrap();
                                     let grammar = store.load_language(grammar_name, &wasm_bytes);
@@ -970,7 +968,7 @@ impl LanguageRegistry {
                 }
             }
         } else {
-            tx.send(Err(Arc::new(anyhow!("no such grammar {}", name))))
+            tx.send(Err(Arc::new(anyhow!("no such grammar {name}"))))
                 .ok();
         }