Make improvements based on OpenZeppelin's updates to their MetaTransactions implementation #1000
Description
OpenZeppelin have released v5 of their contracts: https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v5.0.0
It includes a number of updates to their MetaTransactions implementation, which may be good to use to improve OpenGSN's implementation.
OpenGSN's implementation is still preferred because OpenZeppelin makes forwarder immutable.