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/text_system.rs

@@ -16,7 +16,7 @@ use crate::{
     Bounds, DevicePixels, Hsla, Pixels, PlatformTextSystem, Point, Result, SharedString, Size,
     StrikethroughStyle, UnderlineStyle, px,
 };
-use anyhow::anyhow;
+use anyhow::{Context as _, anyhow};
 use collections::FxHashMap;
 use core::fmt;
 use derive_more::Deref;
@@ -100,7 +100,7 @@ impl TextSystem {
         fn clone_font_id_result(font_id: &Result<FontId>) -> Result<FontId> {
             match font_id {
                 Ok(font_id) => Ok(*font_id),
-                Err(err) => Err(anyhow!("{}", err)),
+                Err(err) => Err(anyhow!("{err}")),
             }
         }
 
@@ -174,7 +174,7 @@ impl TextSystem {
         let glyph_id = self
             .platform_text_system
             .glyph_for_char(font_id, character)
-            .ok_or_else(|| anyhow!("glyph not found for character '{}'", character))?;
+            .with_context(|| format!("glyph not found for character '{character}'"))?;
         let bounds = self
             .platform_text_system
             .typographic_bounds(font_id, glyph_id)?;
@@ -188,7 +188,7 @@ impl TextSystem {
         let glyph_id = self
             .platform_text_system
             .glyph_for_char(font_id, ch)
-            .ok_or_else(|| anyhow!("glyph not found for character '{}'", ch))?;
+            .with_context(|| format!("glyph not found for character '{ch}'"))?;
         let result = self.platform_text_system.advance(font_id, glyph_id)?
             / self.units_per_em(font_id) as f32;