During evaluation of codeblocks, we start off with an iteration of
nodes, and then while evaluating them we may update the global
self.current_node context. When catching and formatting errors, we
didn't take into account that the node might be updated from the
original top-level iteration.
Switch to formatting errors using self.current_node instead, to ensure
we can point at the likely most-accurate actual cause of an error.
Also update the current node in a few more places, so that function
calls always see the function call as the current node, even if the most
recently parsed node was an argument to the function call.
Fixes#11643
Jussi Pakkanen
Eli Schwartz
Dylan Baker