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/dap_adapters/src/gdb.rs

@@ -1,6 +1,6 @@
 use std::{collections::HashMap, ffi::OsStr};
 
-use anyhow::{Result, bail};
+use anyhow::{Context as _, Result, bail};
 use async_trait::async_trait;
 use dap::{StartDebuggingRequestArguments, adapters::DebugTaskDefinition};
 use gpui::AsyncApp;
@@ -78,7 +78,7 @@ impl DebugAdapter for GdbDebugAdapter {
             .which(OsStr::new("gdb"))
             .await
             .and_then(|p| p.to_str().map(|s| s.to_string()))
-            .ok_or(anyhow!("Could not find gdb in path"));
+            .context("Could not find gdb in path");
 
         if gdb_path.is_err() && user_setting_path.is_none() {
             bail!("Could not find gdb path or it's not installed");