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/src/db/tables/project.rs

@@ -1,5 +1,5 @@
 use crate::db::{ProjectId, Result, RoomId, ServerId, UserId};
-use anyhow::anyhow;
+use anyhow::Context as _;
 use rpc::ConnectionId;
 use sea_orm::entity::prelude::*;
 
@@ -18,10 +18,10 @@ impl Model {
     pub fn host_connection(&self) -> Result<ConnectionId> {
         let host_connection_server_id = self
             .host_connection_server_id
-            .ok_or_else(|| anyhow!("empty host_connection_server_id"))?;
+            .context("empty host_connection_server_id")?;
         let host_connection_id = self
             .host_connection_id
-            .ok_or_else(|| anyhow!("empty host_connection_id"))?;
+            .context("empty host_connection_id")?;
         Ok(ConnectionId {
             owner_id: host_connection_server_id.0 as u32,
             id: host_connection_id as u32,