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/semantic_version/src/semantic_version.rs

@@ -7,7 +7,7 @@ use std::{
     str::FromStr,
 };
 
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result};
 use serde::{Deserialize, Serialize, de::Error};
 
 /// A [semantic version](https://semver.org/) number.
@@ -54,15 +54,15 @@ impl FromStr for SemanticVersion {
         let mut components = s.trim().split('.');
         let major = components
             .next()
-            .ok_or_else(|| anyhow!("missing major version number"))?
+            .context("missing major version number")?
             .parse()?;
         let minor = components
             .next()
-            .ok_or_else(|| anyhow!("missing minor version number"))?
+            .context("missing minor version number")?
             .parse()?;
         let patch = components
             .next()
-            .ok_or_else(|| anyhow!("missing patch version number"))?
+            .context("missing patch version number")?
             .parse()?;
         Ok(Self {
             major,