feat: add PathAt code context query (#2232)

This is used for custom paste scripts

- by pattern: e.g. `$root`
- by code: e.g. `{ root }`
- on conflict callback: e.g. `{ (dir: root, on-conflict: root + "/" +
random() + ".png") }`

crates/tinymist-std/src/error.rs

@@ -395,6 +395,19 @@ impl<T, E: std::fmt::Display> WithContextUntyped<T> for Result<T, E> {
     }
 }
 
+impl<T> WithContextUntyped<T> for Option<T> {
+    fn context_ut(self, loc: &'static str) -> Result<T> {
+        self.ok_or_else(|| Error::new(loc, ErrKind::None, None))
+    }
+
+    fn with_context_ut<F>(self, loc: &'static str, f: F) -> Result<T>
+    where
+        F: FnOnce() -> Option<Box<[(&'static str, String)]>>,
+    {
+        self.ok_or_else(|| Error::new(loc, ErrKind::None, f()))
+    }
+}
+
 /// The error prelude.
 pub mod prelude {