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/vim/src/command.rs

@@ -1,4 +1,4 @@
-use anyhow::{Result, anyhow};
+use anyhow::Result;
 use collections::HashMap;
 use command_palette_hooks::CommandInterceptResult;
 use editor::{
@@ -675,10 +675,10 @@ impl Position {
                 let Some(Mark::Local(anchors)) =
                     vim.get_mark(&name.to_string(), editor, window, cx)
                 else {
-                    return Err(anyhow!("mark {} not set", name));
+                    anyhow::bail!("mark {name} not set");
                 };
                 let Some(mark) = anchors.last() else {
-                    return Err(anyhow!("mark {} contains empty anchors", name));
+                    anyhow::bail!("mark {name} contains empty anchors");
                 };
                 mark.to_point(&snapshot.buffer_snapshot)
                     .row