Validates that all references to a variable (pre-SSA) are consistently "local"
references or "context" references. Ie, if a variable is declared as
DeclareContext, any accesses must be eg LoadContext or StoreContext, not
LoadLocal/StoreLocal. This will help with the issue from #2577 (assuming that we
know a variable _is_ a context variable) but also provides a more precise
bailout for an existing case with destructuring assignment to a context
variable.