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/gpui/src/svg_renderer.rs

@@ -1,5 +1,4 @@
 use crate::{AssetSource, DevicePixels, IsZero, Result, SharedString, Size};
-use anyhow::anyhow;
 use resvg::tiny_skia::Pixmap;
 use std::{
     hash::Hash,
@@ -56,9 +55,7 @@ impl SvgRenderer {
     }
 
     pub(crate) fn render(&self, params: &RenderSvgParams) -> Result<Option<Vec<u8>>> {
-        if params.size.is_zero() {
-            return Err(anyhow!("can't render at a zero size"));
-        }
+        anyhow::ensure!(!params.size.is_zero(), "can't render at a zero size");
 
         // Load the tree.
         let Some(bytes) = self.asset_source.load(&params.path)? else {