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/collab_ui/src/collab_panel.rs

@@ -3,6 +3,7 @@ mod contact_finder;
 
 use self::channel_modal::ChannelModal;
 use crate::{CollaborationPanelSettings, channel_view::ChannelView, chat_panel::ChatPanel};
+use anyhow::Context as _;
 use call::ActiveCall;
 use channel::{Channel, ChannelEvent, ChannelStore};
 use client::{ChannelId, Client, Contact, User, UserStore};
@@ -388,9 +389,7 @@ impl CollabPanel {
             Some(serialization_key) => cx
                 .background_spawn(async move { KEY_VALUE_STORE.read_kvp(&serialization_key) })
                 .await
-                .map_err(|_| {
-                    anyhow::anyhow!("Failed to read collaboration panel from key value store")
-                })
+                .context("reading collaboration panel from key value store")
                 .log_err()
                 .flatten()
                 .map(|panel| serde_json::from_str::<SerializedCollabPanel>(&panel))