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/sqlez/src/migrations.rs

@@ -6,7 +6,7 @@
 
 use std::ffi::CString;
 
-use anyhow::{Context as _, Result, anyhow};
+use anyhow::{Context as _, Result};
 use indoc::{formatdoc, indoc};
 use libsqlite3_sys::sqlite3_exec;
 
@@ -69,14 +69,14 @@ impl Connection {
                         // Migration already run. Continue
                         continue;
                     } else {
-                        return Err(anyhow!(formatdoc! {"
-                            Migration changed for {} at step {}
+                        anyhow::bail!(formatdoc! {"
+                            Migration changed for {domain} at step {index}
 
                             Stored migration:
-                            {}
+                            {completed_migration}
 
                             Proposed migration:
-                            {}", domain, index, completed_migration, migration}));
+                            {migration}"});
                     }
                 }