message: Add look_up_span to context
  Summary: Useful function since the codemap isn't available outside this library.
diff: @@ -23,7 +23,7 @@ use crate::{
  eval::call_stack::CallStack,
  values::{FrozenHeap, Heap, Value, ValueRef, Walker},
  };
  -use codemap::{CodeMap, Span};
  +use codemap::{CodeMap, Span, SpanLoc};
  use gazebo::any::AnyLifetime;
  use std::{mem, sync::Arc};
  @@ -111,6 +111,10 @@ impl<'v, 'a> EvaluationContext<'v, 'a> {
  }
  }
  + pub fn look_up_span(&self, span: Span) -> SpanLoc {
  + self.codemap.look_up_span(span)
  + }
  +
  /// Called to add an entry to the call stack, from the caller.
  /// Called for all types of function (including those written in Rust)
  pub(crate) fn with_call_stack<R>(
  