The translation of `IsExpr` created a sanity check to fail since it generated
a Phi node that had only one source: if a variable was declared as part of the `IsExpr`, a conditional branch was generated, and the variable was defined only in the true successor; this has been changes so that the declaration happens before the conditional branch, and the variable is uninitialized (this removed the need for the `isInitializedByElement` predicate from `TranslatedDeclarationBase`, so that has been removed) and only the assignment happens in the true successor block (so now the two inputs of the Phi node are the result of the `Uninitialized` instruction and the `Store` instruction from the true successor block).
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