Add missing pop_begin/pop_end for mapping types (#1173)

I found this additional required fix after merging #1159. This is so
bindings can be processed for files with using directives on mapping
types without crashing. We want to merge this before #1149 to get a
meaningful baseline before those fixes are applied.

crates/solidity/inputs/language/bindings/rules.msgb

@@ -767,6 +767,8 @@ inherit .lexical_scope
 @type_name [TypeName @mapping [MappingType]] {
   let @type_name.type_ref = @mapping.lexical_scope
   let @type_name.output = @mapping.output
+  let @type_name.pop_begin = @mapping.pop_begin
+  let @type_name.pop_end = @mapping.pop_end
 }
 
 
@@ -845,6 +847,12 @@ inherit .lexical_scope
 
   ; resolve the value type through our scope
   edge @value_type.type_ref -> @mapping.lexical_scope
+
+  ; We use the value_type's definition path as our own because it's needed when
+  ; a mapping is the target of a `using` directive. It's not correct, but we
+  ; don't have the analog referencing path either.
+  let @mapping.pop_begin = @value_type.pop_begin
+  let @mapping.pop_end = @value_type.pop_end
 }