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/text/src/text.rs

@@ -11,7 +11,7 @@ mod tests;
 mod undo_map;
 
 pub use anchor::*;
-use anyhow::{Context as _, Result, anyhow};
+use anyhow::{Context as _, Result};
 use clock::LOCAL_BRANCH_REPLICA_ID;
 pub use clock::ReplicaId;
 use collections::{HashMap, HashSet};
@@ -1586,7 +1586,7 @@ impl Buffer {
         async move {
             for mut future in futures {
                 if future.recv().await.is_none() {
-                    Err(anyhow!("gave up waiting for edits"))?;
+                    anyhow::bail!("gave up waiting for edits");
                 }
             }
             Ok(())
@@ -1615,7 +1615,7 @@ impl Buffer {
         async move {
             for mut future in futures {
                 if future.recv().await.is_none() {
-                    Err(anyhow!("gave up waiting for anchors"))?;
+                    anyhow::bail!("gave up waiting for anchors");
                 }
             }
             Ok(())
@@ -1635,7 +1635,7 @@ impl Buffer {
         async move {
             if let Some(mut rx) = rx {
                 if rx.recv().await.is_none() {
-                    Err(anyhow!("gave up waiting for version"))?;
+                    anyhow::bail!("gave up waiting for version");
                 }
             }
             Ok(())