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/debugger_ui/src/session/running/console.rs

@@ -278,7 +278,7 @@ impl CompletionProvider for ConsoleQueryBarCompletionProvider {
         _completion_indices: Vec<usize>,
         _completions: Rc<RefCell<Box<[Completion]>>>,
         _cx: &mut Context<Editor>,
-    ) -> gpui::Task<gpui::Result<bool>> {
+    ) -> gpui::Task<anyhow::Result<bool>> {
         Task::ready(Ok(false))
     }
 
@@ -289,7 +289,7 @@ impl CompletionProvider for ConsoleQueryBarCompletionProvider {
         _completion_index: usize,
         _push_to_history: bool,
         _cx: &mut Context<Editor>,
-    ) -> gpui::Task<gpui::Result<Option<language::Transaction>>> {
+    ) -> gpui::Task<anyhow::Result<Option<language::Transaction>>> {
         Task::ready(Ok(None))
     }