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/extension/src/extension_builder.rs

@@ -1,7 +1,7 @@
 use crate::{
     ExtensionLibraryKind, ExtensionManifest, GrammarManifestEntry, parse_wasm_extension_version,
 };
-use anyhow::{Context as _, Result, anyhow, bail};
+use anyhow::{Context as _, Result, bail};
 use async_compression::futures::bufread::GzipDecoder;
 use async_tar::Archive;
 use futures::io::BufReader;
@@ -134,7 +134,7 @@ impl ExtensionBuilder {
         extension_dir: &Path,
         manifest: &mut ExtensionManifest,
         options: CompileExtensionOptions,
-    ) -> Result<(), anyhow::Error> {
+    ) -> anyhow::Result<()> {
         self.install_rust_wasm_target_if_needed()?;
 
         let cargo_toml_content = fs::read_to_string(extension_dir.join("Cargo.toml"))?;
@@ -429,7 +429,7 @@ impl ExtensionBuilder {
 
         let inner_dir = fs::read_dir(&tar_out_dir)?
             .next()
-            .ok_or_else(|| anyhow!("no content"))?
+            .context("no content")?
             .context("failed to read contents of extracted wasi archive directory")?
             .path();
         fs::rename(&inner_dir, &wasi_sdk_dir).context("failed to move extracted wasi dir")?;
@@ -588,7 +588,7 @@ fn populate_defaults(manifest: &mut ExtensionManifest, extension_path: &Path) ->
                     let grammar_name = grammar_path
                         .file_stem()
                         .and_then(|stem| stem.to_str())
-                        .ok_or_else(|| anyhow!("no grammar name"))?;
+                        .context("no grammar name")?;
                     if !manifest.grammars.contains_key(grammar_name) {
                         manifest.grammars.insert(
                             grammar_name.into(),