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/language/src/buffer.rs

@@ -17,7 +17,7 @@ use crate::{
     task_context::RunnableRange,
     text_diff::text_diff,
 };
-use anyhow::{Context as _, Result, anyhow};
+use anyhow::{Context as _, Result};
 use async_watch as watch;
 pub use clock::ReplicaId;
 use clock::{AGENT_REPLICA_ID, Lamport};
@@ -816,13 +816,11 @@ impl Buffer {
         message: proto::BufferState,
         file: Option<Arc<dyn File>>,
     ) -> Result<Self> {
-        let buffer_id = BufferId::new(message.id)
-            .with_context(|| anyhow!("Could not deserialize buffer_id"))?;
+        let buffer_id = BufferId::new(message.id).context("Could not deserialize buffer_id")?;
         let buffer = TextBuffer::new(replica_id, buffer_id, message.base_text);
         let mut this = Self::build(buffer, file, capability);
         this.text.set_line_ending(proto::deserialize_line_ending(
-            rpc::proto::LineEnding::from_i32(message.line_ending)
-                .ok_or_else(|| anyhow!("missing line_ending"))?,
+            rpc::proto::LineEnding::from_i32(message.line_ending).context("missing line_ending")?,
         ));
         this.saved_version = proto::deserialize_version(&message.saved_version);
         this.saved_mtime = message.saved_mtime.map(|time| time.into());