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/project/src/debugger/dap_command.rs

@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use anyhow::{Ok, Result, anyhow};
+use anyhow::{Context as _, Ok, Result};
 use dap::{
     Capabilities, ContinueArguments, ExceptionFilterOptions, InitializeRequestArguments,
     InitializeRequestArgumentsPathFormat, NextArguments, SetVariableResponse, SourceBreakpoint,
@@ -1766,7 +1766,7 @@ impl DapCommand for LocationsCommand {
             source: response
                 .source
                 .map(<dap::Source as ProtoConversion>::from_proto)
-                .ok_or_else(|| anyhow!("Missing `source` field in Locations proto"))?,
+                .context("Missing `source` field in Locations proto")?,
             line: response.line,
             column: response.column,
             end_line: response.end_line,