Rules with existential variables must retain \exists and restore variable names

[jberthold]

Existentials at the top of the RHS of rewrite rules are separated and the variables renamed (to avoid name clashes).
When such a rule is applied, the variables need to be renamed back in the result term, and the \exists re-added.

[goodlyrottenapple]

Came up in foundry tests

ERROR 2023-06-28 10:42:09,890 kevm_pyk.utils - Proof crashed: ERC20Test.testApproveFailure_1:f722834c55b10126e5ef08407c904c5f163a62067de30d87f4f11173399ecbc5
Expected identifier, got: Ex#Var'Ques'STORAGE